Remove code variants for Qt < 5.8 and KF < 5.50

GIT_SILENT
1 job for !110 with version_check in 60 minutes (queued for 43 minutes and 44 seconds)
detached
Status Job ID Name Coverage
  Build
failed #35195
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
        Start  86: test_qmljsdeclarations
kf5.kinit.klauncher: new app ":1.49"
kf5.kinit.klauncher: new app "org.kdevelop.kdevplatform-lock-871d374e-734b-4007-b4c7-54fd38334e0b"
86/124 Test #86: test_qmljsdeclarations .................. Passed 3.83 sec
Start 87: test_files
kf5.kinit.klauncher: new app ":1.50"
kf5.kinit.klauncher: new app "org.kdevelop.kdevplatform-lock-4c149daa-6dff-4aa0-8a91-e7b33dfe6fc0"
Pulling docker image gitlab/gitlab-runner-helper:x86_64-003fe500 ...
ERROR: Job failed: execution took longer than 1h0m0s seconds