Remove utils.FileUtils

[domdomegg]

Description (required)

Removes utils/FileUtils to simplify project organisation, particularly as there are two (the other is upload.FileUtils) and none of the code in it is actually used.

It had 2 methods, both of which were used once. Also the function (in ContributionUtils) that calls them is never used. However in case it is useful in the future I've moved the methods to ContributionUtils. I also improved the structure of ContributionUtils.decideTempDestinationFileName slightly.

Tests performed (required)

All automated tests pass

Tested 2.9.0-debug-delete-utils-fileutils~08b5f85e on Samsung Galaxy S6 with API level 25.

[codecov-io]

Codecov Report

Merging #2118 into master will increase coverage by <.01%.
The diff coverage is 0%.

@@            Coverage Diff            @@
##           master   #2118      +/-   ##
=========================================
+ Coverage    5.49%    5.5%   +<.01%     
=========================================
  Files         231     230       -1     
  Lines       11546   11536      -10     
  Branches     1075    1074       -1     
=========================================
  Hits          635     635              
+ Misses      10859   10849      -10     
  Partials       52      52

Impacted Files	Coverage Δ
...a/fr/free/nrw/commons/utils/ContributionUtils.java	7.14% <0%> (-4.98%)	⬇️

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[maskaravivek]

Thanks for consolidating the FileUtils.