scripts/tags.sh: remove *PCGFLAGS regular expressions

Commit 0a31bc97 (mm: memcontrol: rewrite uncharge API)
removed the macros {TEST,SET,CLEAR,TESTCLEAR}PCFLAG.  Remove
corresponding entries from tags.sh -- in the emacs case they also
produced warnigs because of unmatched '\('.

Signed-off-by: Dirk Gouders <dirk@gouders.net>
Inspired-by: Masatake YAMATO <yamato@redhat.com>
Signed-off-by: Michal Marek <mmarek@suse.cz>