Revert "mail/dovecot: Add FLAVORs for CDB, LDAP, MYSQL, PGSQL, and SQLITE3"

Flavors currently breaks mail/dovecot-pigeonhole,
mail/dovecot-fts-xapian, mail/dovecot-fts-flatcurve.

nc & I (ler) will work to see if we can come to a better way to do this

This reverts commit 0dd69d0adfd2ef48dc949bb2325c2c534117fc29.