MB-366 don't save non eligible coaching number (#230)

* MB-366 don't save non eligible coaching number

This fixes a few little bugs in the system as well as the one listed in
the ticket.

* We no longer make an extra API call to user profile when toggling
coaching
* The user now must toggle coaching off to save a non-eligible phone
number
* If the user changes to another US based phone number, or is not
consented to coaching, the phone number will save as normal.

* Fix weird code

.env.development

@@ -17,4 +17,4 @@ SITE_NAME='edX'
 SUPPORT_URL='http://localhost:18000/support'
 USER_INFO_COOKIE_NAME='edx-user-info'
 # Temporary, Remove this once we are ready to release the feature.
-COACHING_ENABLED=''
+COACHING_ENABLED=true