has_client.cc: fix profile disconnection cleanup

GATT cleanup must be performed on HAS Device before it is removed from
`devices_` list - in other case, GATT queue will not be cleared, and
in the future, if another HAS Device gets the same connection ID, it
will "inherit" pending items - and will be unable to post its own to
GATT queue.

Bug: 356799752
Flag: Exempt, feature not launched yet
Test: atest --host --no-bazel-mode bluetooth_has_test
Change-Id: Id3cdc41b276efa44eb4e15b01f226393fab71e2b