Remove libbluetooth-gdx

ModuleMainloop, ModuleJniloop are thin wrappers on top
of do_in_main_thread, do_in_jni_thread, and are only used
in tests.

Remove the associated tests libbluetooth-gdx-test for
dumpsys and lifecylce due to lack of comment and
documentation (only run in postsubmit).

Bug: 331817295
Test: m com.android.btservices
Flag: EXEMPT, dead code removal
Change-Id: I84d810e3f5a371013e1cc3a17561ccaa66f65164