Rename bluetooth_gd_hci_fuzz_test target to bluetooth_gd_hci_layer_fuzz_test

Since there will be separate targets for separate fuzz tests, and there
will be separate fuzz tests for each module.

convetion: bluetooth_gd_<module>_fuzz_test

Test: fuzz/run --host bluetooth_gd_hci_layer_fuzz_test
Change-Id: I0c0aa26ea821aa5a8e66f298c92c998ea6848e60