Don't clear the calling identity until needed for SmsManager

We were clearing the calling identity in IccSmsInterfaceManager
in order to access CarrierConfigManager. This was causing
us to also clear the calling identity in SMSDispatcher, which
needs the UID of the caller.

Bug: 129909610
Test: manual
Change-Id: I9cc0c04a876c30aa7032b0b84acb580ed95ea8a7