email: deactivate sync of deleted secure accounts

There is a security hold (describe here https://android-review.googlesource.com/#/c/100460/) when a user
deactivate the email device administrator. In this case the data is deleted but the account can still
be synced.
AOSP advise was to set the hold flag over the account.

Change-Id: Ibde2e5ca13e70c527feffb906f30e61068b158be
Signed-off-by: Jorge Ruesga <jorge@ruesga.com>