has_client.cc: fix single device disconnection

Before BTA_GATTC_Close is called, DoDisconnectCleanUp() and
devices_.erase() shall be called, preventing second call of disconnect
from GATT.

Bug: 370405555
Bug: 361014973
Test: atest --host --no-bazel-mode HasClientTest
Flag: com.android.bluetooth.flags.hap_connect_only_requested_device
Change-Id: Id1c1944b0ea15a6c0caa10be38092997c98f1cb9