RootCanal: Remove unused test channels in the test environment

HCI, LL and, BLE_LL channels are wrapped in a test channel in the
test environment class, but only the SetUp method is ever called;

this change inlines the SetUp for the afore mentioned channels.

Test: m root-canal
Bug: 279665786
Change-Id: I12c9a38fdd2540094e0143972e496aedf9241501