Drop LLD_UNSAFE=yes.

The port is building fine on 12.0 and HEAD without setting this. The port's
build system is still wrong (i.e. the port still builds the same moc-generate
code in duplicate files), but lld seems to handle this case well.

A proper fix was sent upstream in https://phabricator.kde.org/D24609.

I am not bumping PORTREVISION because this only changes build dependencies.

PR: 228640