This greatly simplifies code and allows to override build date with SOURCE_DATE_EPOCH in order to make builds reproducible. See https://reproducible-builds.org/ for why this is good and https://reproducible-builds.org/specs/source-date-epoch/ for the definition of this variable.
We still use UTC to be independent of timezone.
Without this patch, /usr/lib64/libdigikamcore.so.7.2.0 always varied between clean builds.
This PR was done while working on reproducible builds for openSUSE.