Fix NPE in SmsManager and keep existing behavior

The behavior of SmsManager#sendTextMessage changed,
we are blocking the sending of the SMS if there were no
subscriptions (i.e. no SIM scenario). This change
accidently introduced a NPE scenario in some cases.

Fixed NPE and removed SMS blocking code in SmsManager
to keep existing functionality the same.

Bug: 127338050
Test: atest GtsTelephonyTestCases
Change-Id: I71eefbc8e1619701e1b1d7b12c3c080c4ef376ef