Remove "text/x-diff" alias from supported MIME types

"text/x-diff" is an alias for "text/x-patch" MIME type. Therefore its
glob patterns are identical: "*.diff" and "*.patch". The downside of the
presence of this alias in the SupportedMimeTypes list is that
LanguageController must either match all filenames against duplicate
patterns (as it does now) or detect and remove these duplicate patterns,
which would entail unnecessary extra code and still some run-time work.

There are many "x-patch" uses in KDevelop code base, but this was the
only use of "x-diff". That is why I don't think this alias will be
missed by anyone.
1 job for !150 with remove-text-x-diff-mime-type-alias in 60 minutes (queued for 1 second)
latest detached
Status Job ID Name Coverage
  Build
failed #61993
linux kf5-qt5 qt5.12

01:00:00

 
Name Stage Failure
failed
linux kf5-qt5 qt5.12 Build The script exceeded the maximum execution time set for the job
kf.kio.slaves.file: copy() QUrl("file:///builds/igorkushnir/kdevelop/plugins/cmake/tests/manual/relative_paths/out/relative_paths.kdev4") to QUrl("file:///tmp/test_cmakemanager.mMMIXp") mode= -1
kf.kio.slaves.file: copy() QUrl("file:///builds/igorkushnir/kdevelop/plugins/cmake/tests/manual/target_include_directories/target_include_directories.kdev4") to QUrl("file:///tmp/test_cmakemanager.gOonGa") mode= -1
kf.kio.slaves.file: copy() QUrl("file:///builds/igorkushnir/kdevelop/plugins/cmake/tests/manual/target_includes/target_includes.kdev4") to QUrl("file:///tmp/test_cmakemanager.ZfGadt") mode= -1
kf.kio.slaves.file: copy() QUrl("file:///builds/igorkushnir/kdevelop/plugins/cmake/tests/manual/defines/defines.kdev4") to QUrl("file:///tmp/test_cmakemanager.FiTieu") mode= -1
kf.kio.slaves.file: copy() QUrl("file:///builds/igorkushnir/kdevelop/plugins/cmake/tests/manual/custom_target_sources/custom_target_sources.kdev4") to QUrl("file:///tmp/test_cmakemanager.KITcjc") mode= -1
kf.kio.slaves.file: copy() QUrl("file:///builds/igorkushnir/kdevelop/plugins/cmake/tests/manual/conditions_in_subdirectory_based_on_root_variables/conditions_in_subdirectory_based_on_root_variables.kdev4") to QUrl("file:///tmp/test_cmakemanager.YzUdIi") mode= -1
Uploading artifacts for failed job
Pulling docker image gitlab/gitlab-runner-helper:x86_64-a998cacd ...
ERROR: Job failed: execution took longer than 1h0m0s seconds