Bluetooth: Remove unused declaration amp_read_loc_info()

This is introduced in commit 903e4541 but was never implemented.

Fixes: 903e4541 ("Bluetooth: AMP: Use HCI cmd to Read Loc AMP Assoc")
Signed-off-by: Yue Haibing <yuehaibing@huawei.com>
Signed-off-by: Luiz Augusto von Dentz <luiz.von.dentz@intel.com>