fdo#70393: move bluez_bluetooth to a subdir of external

Change-Id: Ia1c5eb2e6c5193256b61ec878abdb648632e1f47
Reviewed-on: https://gerrit.libreoffice.org/6570
Reviewed-by: David Tardon <dtardon@redhat.com>
Tested-by: David Tardon <dtardon@redhat.com>