A2DP: Remove system property check about offloading capability

The A2DP offlaoding capability depends on HAL capabilities and Audio
service perference.

Tag: #refactor
Bug: 243958304
Ignore-AOSP-First: tm-qpr feature
Test: atest net_test_stack:A2dpCodecConfigTest#init
Change-Id: Ic7e7fca6c3c33e3416d7d79cf206bca9bb73e584