Move getPhoneCount implementation back to TelephonyManager.

Moving it inside iTelephony creates problems. Some components call
getPhoneCount during initialization while iTelephony service is not
even running, which will cause phone process to crash.

Bug: 123667461
Test: manual
Change-Id: I097d4694a1b0957420ba4636ed8b4b1b89d63500
Merged-In: I097d4694a1b0957420ba4636ed8b4b1b89d63500