Delete libbt_common

This rust library only exports the method `init_logging`,
which is used solely by the bluetooth_core crate.
`init_logging` is inlined to system/rust/src/utils.rs

Bug: 331817295
Test: m libbluetooth_core_rs
Flag: EXEMPT, dead code removal
Change-Id: Ib8fce44be854f095a3a95324df102ef060717084