Email: Remove unnecessary enable sync size setting

* Determine whether sync size limiting is enabled based on the sync size
  setting itself.
* Database column must remain, as there is no support for deleting
  columns in SQLite.

Change-Id: Ica7808de03dd76bf53f4cfbe8618bacb4859d1b1
Merge branch 'cm-11.0' of git://github.com/CyanogenMod/android_packages_apps_Email into cm-11.0