Retire deprecations

[SpacemanPaul]

Reason for this pull request

Many features/syntax have been flagged as deprecated in previous releases. Some have been deprecated for quite some time.

Proposed changes

Deprecated features/syntax removed in this PR:

• datacube.helpers.write_geotiff (Deprecated in v1.8.0)
• auto_match argument to dc.index.datasets.add() (Deprecated in v1.6.0)
• celery executor (Deprecated in v1.8.7)
• deriving CRS from datum/zone (Deprecated in 1.8.0)
• support for broken/mossing geospatial driver from rasterio reader. (Deprecated in 1.8.0)
• rebuild_all argument to `dc.index.metadata_types.check_field_index(). (Deprecated in 1.5.4)
• source policy support in dc.index.datasets.add(). (Deprecated in 1.5.4 (!))

Corresponding test cases also removed.

Deprecated behaviour NOT removed in this PR:

• virtual products transforms deprecated in PR deprecate Rename, Select and ToFloat transformations #1263

• Tests added / passed

• Fully documented, including docs/about/whats_new.rst for all changes

[codecov]

Codecov Report

Merging #1275 (5ed060e) into develop (82ed29c) will decrease coverage by 0.10%.
The diff coverage is 85.71%.

@@             Coverage Diff             @@
##           develop    #1275      +/-   ##
===========================================
- Coverage    93.58%   93.48%   -0.11%     
===========================================
  Files          129      128       -1     
  Lines        13203    12952     -251     
===========================================
- Hits         12356    12108     -248     
+ Misses         847      844       -3     

Impacted Files	Coverage Δ
datacube/executor.py	65.08% <ø> (+0.55%)	⬆️
datacube/helpers.py	33.33% <ø> (-42.28%)	⬇️
datacube/index/memory/_datasets.py	89.64% <ø> (-0.22%)	⬇️
datacube/index/null/_datasets.py	100.00% <ø> (ø)
datacube/index/postgis/_datasets.py	94.47% <ø> (-0.12%)	⬇️
datacube/index/postgres/_datasets.py	94.75% <ø> (-0.12%)	⬇️
datacube/model/__init__.py	95.89% <ø> (-0.30%)	⬇️
datacube/scripts/dataset.py	88.13% <ø> (-0.11%)	⬇️
datacube/storage/_rio.py	93.05% <50.00%> (-1.07%)	⬇️
datacube/index/abstract.py	96.17% <100.00%> (ø)
... and 12 more

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