Fixes #7270/BZ1131661: remove GMT from new sync plan form.

Sync plan start time was listed as being in GMT and this is not
the case.  This commit removes the timezone designation.

http://projects.theforeman.org/issues/7270
https://bugzilla.redhat.com/show_bug.cgi?id=1131661
Did you mean to get rid of the actual start time too?