Announcement Button Displays incorrect number of users

[choquette33]

Correct the number that is displayed in the "Send to ### volunteers" to reflect active users with a valid phone number. I believe that right now it displays the active and inactive combined total, regardless of whether there is a phone number associated with their account.

For example, in Madagascar there are only 146 active users, but the button displays 232

[choquette33]

related to #496