Remove TelephonyManager#isVoiceCapable calls from Telecom

Remove references to TelephonyManager#isVoiceCapable from Telecom.
Telecom now has a separate FEATURE_TELECOM feature, so it makes no
sense to call into TelephonyManager#isVoiceCapable.

Test: Updated unit tests.
Fixes: 228452834
Change-Id: I2cd67d957b95556cb6b396015894ff901f869d65