Remove webcal protocol file

The location of the KIO slave has changed for quite a while and the file
is not working anymore. Considering that there are no bug reports and
nothing depends on that file being installed we can just remove it.
2 jobs for master in 13 minutes (queued for 33 minutes and 11 seconds)
Status Name Job ID Coverage
  Build
passed build_clazy_clang_tidy #109836

00:08:49

passed linux kf5-qt5 qt5.15 #109835

00:04:11

7.0%