Bug 1038131 - latin.js failed to deactivate and continue to respond to
selectionchange.
 - Remove the event listener for 'selectionchange' in IME's deactivate().
Merge pull request #21807 from RudyLu/keyboard/Bug1038131-remove_selectionchange_listener

Bug 1038131 - latin.js failed to deactivate and continue to respond to
r=timdream.