rm, find -delete: fix removing symlinks with uchg/uappnd set.

Formerly, this tried to clear the flags on the symlink's target
instead of the symlink itself.

As before, this only happens for root or for the unlink(1) variant of rm.

PR: bin/111226 (part of)
Submitted by: Martin Kammerhofer
Approved by: ed (mentor)
MFC after: 3 weeks