Remove duplicate tests for TooManyFunctions rule

[schalkms]

• the test cases in the case files are already covered by other tests
• remove the unnecessary case files

[codecov-io]

Codecov Report

Merging #2338 into master will not change coverage.
The diff coverage is n/a.

@@            Coverage Diff            @@
##             master    #2338   +/-   ##
=========================================
  Coverage     81.87%   81.87%           
+ Complexity     2119     2118    -1     
=========================================
  Files           348      348           
  Lines          6047     6047           
  Branches       1108     1108           
=========================================
  Hits           4951     4951           
  Misses          512      512           
  Partials        584      584

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