Revise seamless transcoding optimization flags

These flags determine if we bypass transcoding in several platform
media classes.

We previously, had non-perssitent, default-false flags for each
framework class.

Now, we have one persistent default-true 'optimize' flag:
persist.sys.fuse.transcode_optimize.

Of course, if the global transcode flag, persist.sys.fuse.transcode is
off, the code is a no-op.

Bug: 158465539
Test: Manual
Change-Id: Ie1442213d0744888bac45b43ad8a07f0ebf55066