WL#8216: Deprecate and remove the sync_frm sysvar

This worklog is about deprecation and removal of the sync_frm sysvar.
http://dev.mysql.com/doc/refman/5.7/en/server-system-
variables.html#sysvar_sync_frm

"If this variable is set to 1, when any nontemporary table is created its .frm
file is synchronized to disk (using fdatasync()). This is slower but safer in
case of a crash. The default is 1."

With the new data dictionary and the removal of .FRM, .TRG and .TRN files,
this option no longer makes any sense.

We will deprecate in 5.7 and remove in 5.8 together with the new DD.

User Documentation
==================

http://dev.mysql.com/doc/relnotes/mysql/5.7/en/news-5-7-6.html
http://dev.mysql.com/doc/refman/5.7/en/server-system-
variables.html#sysvar_sync_frm

I-1: Accessing the sync_frm system variable will give a deprecation warning
     in 5.7 and "unknown system variable" error in 5.8.