staging/android: sync: remove interfaces that are not used

These interfaces are not used nor have plans to be used in the near
future so remove them for a cleaner solution before de-staging the sync
framework.

Signed-off-by: Gustavo Padovan <gustavo.padovan@collabora.co.uk>
Reviewed-by: Maarten Lankhorst <maarten.lankhorst@linux.intel.com>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>