Refactor SMSDispatcher and friends.

Right now ImsSmsDispatcher acts as both a controller that
has pointers to gsm and cdma dispatchers as well as a
dispatcher itself by extending SmsDispatcher, making the
hirarechy convulted.

For example some methods it override but should not invoke
and some methods cdma and gsm dispatchers override but should
not invoke.

Instead this CL converts ImsSmsDispatcher into a proper controller
in preparation for adding a proper ImsSmsDispatcher.

While here also cleaned up a few things like removing duplicate code.

Test: send/receive ims and non-ims manually
Bug: 69846044
Merged-In: Iee97dbaf2284a04eebad28d3a8da627c283cc8a6
Change-Id: Iee97dbaf2284a04eebad28d3a8da627c283cc8a6