kdevplatform: remove About data feature

With KDevPlatform no longer a stand-alone product, but effectively
only an internal architecture platform of KDevelop, the About data
and the About KDevPlatform dialog no longer make sense

Any author information is merged with the one of the KDevelop app,
which it already almost was a subset of.
1 job for !84 with removeplatformaboutdata in 35 minutes and 16 seconds (queued for 1 second)
Status Job ID Name Coverage
failed #27457
linux kf5-qt5 qt5.12


Name Stage Failure
linux kf5-qt5 qt5.12 Build
[ 96%] Linking CXX executable test_filteredproblemstore
[ 96%] Built target test_filteredproblemstore
[ 96%] Linking CXX executable test_shellbuddy
[ 96%] Built target test_shellbuddy
make: *** [Makefile:141: all] Error 2
Uploading artifacts...
WARNING: JUnitTestResults.xml: no matching files
ERROR: No files to upload
ERROR: Job failed: exit code 1