has_client.cc: add missing BTA_GATTC_CancelOpen in Disconnect

Registrations for connection shall be removed when disconnecting.

Bug: 370405555
Bug: 361014973
Test: atest --host --no-bazel-mode HasClientTest
Flag: com.android.bluetooth.flags.hap_connect_only_requested_device
Change-Id: I03ee326147f6d2e56fb0fd684a14ebd857615f5d