Remove sms_user_get_uid()

Summary

Returns the uid of the owner of a number.

function sms_user_get_uid($number, $status = NULL);

Does not make sense anymore as a phone number could potentially be associated with more than one entity.

The current usage of this function includes:

• Associating a user with a sms_track row. - todo
• Looking up sleep preference and/or opt out. - Will be replaced by #2677676: Automated Messages & Sleep

Proposition

A new method on phone number provider should be added to look up a phone number with a entity type.

Need to double down on enforcing unique phone numbers. (related #1363942: Enforce unique phone numbers)