etc/mail actually applies to MK_SENDMAIL, not MK_MAIL


git-svn-id: svn+ssh://svn.freebsd.org/base/head@275270 ccf9f872-aa2e-dd11-9fc8-001c23d0bc1f
Revert r275270

MK_MAIL applies to MK_SENDMAIL and a number of other knobs. r275270 incorrectly
applied it to only MK_SENDMAIL


git-svn-id: svn+ssh://svn.freebsd.org/base/head@275271 ccf9f872-aa2e-dd11-9fc8-001c23d0bc1f