Remove the broken and unused get_deprecated_arg_names

[carmocca]

What does this PR do?

Follow-up to #13693 (comment)

For the historians, this was added in #1147

Does your PR introduce any breaking changes? If yes, please list them.

Removes the broken and unused method.

No public usage: https://grep.app/search?q=get_deprecated_arg_names

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cc @justusschock @awaelchli @rohitgr7 @Borda

[codecov]

Codecov Report

Merging #14415 (5c74d9d) into master (d4bcafa) will increase coverage by 25%.
The diff coverage is n/a.

@@            Coverage Diff            @@
##           master   #14415     +/-   ##
=========================================
+ Coverage      51%      76%    +25%     
=========================================
  Files         332      332             
  Lines       26890    26915     +25     
=========================================
+ Hits        13786    20451   +6665     
+ Misses      13104     6464   -6640