stagefright: Allow devices to use older widevine blobs

Many devices have widevine plugs build with an older MediaSource
interface.  Trying to use them fails when using secure buffers
because the newer library ends up calling the destructor instead
of setBuffers.  Provide an #ifdef to accommodate these older
blobs.

Makes it possible to fix JIRA-4944 on hammerhead.

Change-Id: I4ce24a16f3eceab0c4def4b09850ed569eb392ab