[Minor] Remove FAKE_REPLY_C and move FAKE_REPLY rule to regexp module

[Minor] Remove FAKE_REPLY_C and move FAKE_REPLY rule to regexp module

FAKE_REPLY_C rule no longer works because MUA it used are no longer used
(and ones which are used changed headers they add).  In theory one can
test all popular modern MUA and see which add only References, which
only In-Reply-To and which add both headers.  But it will be a lot of
work to maintain such rule up to date.  It still has a small number of
hits, but mostly because some spammers use old X-Mailer headers.  This
should be addressed separately.

While here re-create FAKE_REPLY as a regexp module rule - this way it
should be more efficient.