Replace documentation references to SimpleModel with FunctionModel

[omsai]

SimpleModel was removed in 3fc1a52

• I confirmed that the sphinx docs build as expected.
• FYI the pre-commit hook recommended by CONTRIBUTE.rst fails as follows:

[INFO] Initializing environment for https://github.com/psf/black.
[INFO] Initializing environment for https://github.com/pycqa/isort.
[INFO] Initializing environment for https://github.com/nbQA-dev/nbQA.
[INFO] Initializing environment for https://github.com/nbQA-dev/nbQA:black.
[INFO] Initializing environment for https://github.com/nbQA-dev/nbQA:pyupgrade.
[INFO] Initializing environment for https://github.com/nbQA-dev/nbQA:isort.
[INFO] Initializing environment for https://github.com/pre-commit/pre-commit-hooks.
[INFO] Installing environment for https://github.com/psf/black.
[INFO] Once installed this environment will be reused.
[INFO] This may take a few minutes...
[INFO] Installing environment for https://github.com/pycqa/isort.
[INFO] Once installed this environment will be reused.
[INFO] This may take a few minutes...
[INFO] Installing environment for https://github.com/nbQA-dev/nbQA.
[INFO] Once installed this environment will be reused.
[INFO] This may take a few minutes...
[INFO] Installing environment for https://github.com/nbQA-dev/nbQA.
[INFO] Once installed this environment will be reused.
[INFO] This may take a few minutes...
[INFO] Installing environment for https://github.com/nbQA-dev/nbQA.
[INFO] Once installed this environment will be reused.
[INFO] This may take a few minutes...
[INFO] Installing environment for https://github.com/pre-commit/pre-commit-hooks.
[INFO] Once installed this environment will be reused.
[INFO] This may take a few minutes...
black....................................................................Passed
isort (python)...........................................................Passed
isort (cython).......................................(no files to check)Skipped
isort (pyi)..........................................(no files to check)Skipped
nbqa-black...........................................(no files to check)Skipped
nbqa-pyupgrade.......................................(no files to check)Skipped
nbqa-isort...........................................(no files to check)Skipped
check yaml...........................................(no files to check)Skipped
check for added large files..............................................Passed
check for merge conflicts................................................Passed
check for broken symlinks............................(no files to check)Skipped
trim trailing whitespace.................................................Passed
fix end of files.........................................................Passed
detect private key.......................................................Passed
Check style..............................................................Failed
 - hook id: style
 - exit code: 1
 
flake8: install_deps> python -I -m pip install 'black>=22.3.0' 'flake8-bandit>=4.1.1' 'flake8-black>=0.2.3' 'flake8-bugbear>=22.8.23' 'flake8-colors>=0.1.6' 'flake8-comprehensions>=3.2.3' 'flake8-isort>=4.0.0' 'flake8-print>=5.0.0' 'flake8>=3.8.3'
flake8: commands[0]> flake8 pyabc test test_performance setup.py
Unable to find qualified name for module: setup.py
pyabc/acceptor/__init__.py:8:1: BLK100 Black would make changes.
pyabc/acceptor/acceptor.py:443:27: BLK100 Black would make changes.
pyabc/distance/distance.py:72:13: BLK100 Black would make changes.
pyabc/distance/kernel.py:2:1: BLK100 Black would make changes.
pyabc/distance/scale.py:34:1: BLK100 Black would make changes.
pyabc/predictor/predictor.py:484:13: BLK100 Black would make changes.
pyabc/storage/migrations/versions/1_20210219_add_particles_proposal_id.py:8:1: BLK100 Black would make changes.
pyabc/util/par_trafo.py:97:13: BLK100 Black would make changes.
test/base/test_samplers.py:231:69: BLK100 Black would make changes.
test_performance/test_samplerperf.py:163:69: BLK100 Black would make changes.
flake8: exit 1 (3.28 seconds) /Users/pnanda/src/pyABC> flake8 pyabc test test_performance setup.py pid=71418
  flake8: FAIL code 1 (6.92=setup[3.64]+cmd[3.28] seconds)
  evaluation failed :( (6.96 seconds)

• The above Black-related issues don't flag the pyabc/model/model.py that I changed, so I uninstalled the commit hook to create the PR.

[codecov-commenter]

Codecov Report

All modified and coverable lines are covered by tests ✅

Project coverage is 81.65%. Comparing base (6446a77) to head (0d1305b).
Report is 235 commits behind head on develop.

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Additional details and impacted files

@@             Coverage Diff             @@
##           develop     #629      +/-   ##
===========================================
- Coverage    84.08%   81.65%   -2.44%     
===========================================
  Files           91      141      +50     
  Lines         5260     8535    +3275     
===========================================
+ Hits          4423     6969    +2546     
- Misses         837     1566     +729     

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[stephanmg]

Thanks for the fix.