Bug 917028 - [B2G][SMS] Compose an SMS: Unable to add more than one recipient from Contacts r=borja

Remove the classList handling from updateComposerHeader because since version
1.1 we support sending multiple contacts.
Merge pull request #12297 from julienw/917028-add-more-than-1-contact

Bug 917028 - [B2G][SMS] Compose an SMS: Unable to add more than one reci...