[feat] Remove deprecated features for 4.x

[vkarak]

Closes #1917.
Closes #1918.
Closes #2017.

[codecov-commenter]

Codecov Report

Merging #2096 (44c1f33) into 4.x (d2c12f1) will increase coverage by 0.22%.
The diff coverage is 100.00%.

❗ Current head 44c1f33 differs from pull request most recent head bcbdc52. Consider uploading reports for the commit bcbdc52 to get more accurate results

@@            Coverage Diff             @@
##              4.x    #2096      +/-   ##
==========================================
+ Coverage   86.80%   87.03%   +0.22%     
==========================================
  Files          52       52              
  Lines        9232     9137      -95     
==========================================
- Hits         8014     7952      -62     
+ Misses       1218     1185      -33     

Impacted Files	Coverage Δ
reframe/core/pipeline.py	92.43% <ø> (+0.44%)	⬆️
reframe/utility/sanity.py	97.76% <ø> (-0.03%)	⬇️
reframe/core/decorators.py	88.33% <100.00%> (+24.04%)	⬆️
reframe/utility/versioning.py	95.23% <100.00%> (-1.54%)	⬇️

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[jjotero]

Just a minor comment

[ekouts]

1. There are some references to rfm.run_after in reframe/core/launchers, reframe/core/schedulers/__init__.py and reframe/utility/__init__.py that still need to be changed. They are part of documentation.
2. I see a lot of tests using the parameterized_test decorator in the branch. These should be fixed in a different PR, right?
3. There are also many tests using the @sn.sanity_function decorator in the branch. Different PR as well?

[vkarak]

@ekouts I will fix (1). I guess that by saying "tests," you mean ReFrame tests, not unit tests. These should be fixed in different PRs.

[ekouts]

lgtm