Revert "Merge pull request #10018 from huchengtw-moz/sms/Bug_875564_after_attaching_image_sometimes_send_button_is_still_disabled"

Bug 875564 - [MMS] after attaching image, sometimes send button is still disabled. r=steveck-chung

This reverts commit e19c6980de1089af7a120be4b49d49a6bb5d28e4, reversing
changes made to b3dd91ed197f96c698f03e1f67de3a7602d46880.