Remove isServiceConnected() from TelecomManager

isServiceConnected() was being called before uses of getTelecomService()
to ensure that the service was connected before accessing it. However,
isServiceConnected() used getTelecomService() to check if the service
was connected, resulting in unnecessary binder calls.

Bug: 173036057
Bug: 173039862
Test: manual testing (switching between different tabs, calling)
Change-Id: I622464927826d8af1c6e75ed4557580d8723315c