[4.6] Handle only known functions in rm_rf (#5627)

[nicoddemus]

Backport of #5627

Conflicts:

• src/_pytest/pathlib.py

Also had to adapt:

• PermissionError into OSError with appropriate errno
• Change keyword-only argument to **kwargs
• Remove type annotations

[codecov]

Codecov Report

Merging #5691 into 4.6-maintenance will increase coverage by 24.96%.
The diff coverage is 98.43%.

@@                 Coverage Diff                  @@
##           4.6-maintenance    #5691       +/-   ##
====================================================
+ Coverage            71.23%   96.19%   +24.96%     
====================================================
  Files                  115      115               
  Lines                26512    26542       +30     
  Branches              2613     2615        +2     
====================================================
+ Hits                 18886    25533     +6647     
+ Misses                7166      703     -6463     
+ Partials               460      306      -154

Impacted Files	Coverage Δ
testing/test_tmpdir.py	99.14% <100%> (+22.73%)	⬆️
src/_pytest/pathlib.py	91.26% <96%> (+10.35%)	⬆️
src/_pytest/assertion/rewrite.py	95.77% <0%> (+0.81%)	⬆️
testing/test_stepwise.py	100% <0%> (+1.35%)	⬆️
src/_pytest/_code/source.py	91.58% <0%> (+2.33%)	⬆️
src/_pytest/fixtures.py	97.55% <0%> (+2.44%)	⬆️
src/_pytest/_code/code.py	95.5% <0%> (+2.56%)	⬆️
src/_pytest/terminal.py	93.44% <0%> (+2.64%)	⬆️
src/_pytest/mark/__init__.py	97.61% <0%> (+3.57%)	⬆️
... and 77 more

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