Revert "[Media Session] [1/4] Move MediaMetadata to service"

This reverts commit 93ee1837006400a4fde789787d70a7f09905cce8.

Reason for revert:

Findit (https://goo.gl/kROfz5) identified CL at revision 605481 as the
culprit for failures in the build cycles as shown on:
https://findit-for-me.appspot.com/waterfall/culprit?key=ag9zfmZpbmRpdC1mb3ItbWVyRAsSDVdmU3VzcGVjdGVkQ0wiMWNocm9taXVtLzkzZWUxODM3MDA2NDAwYTRmZGU3ODk3ODdkNzBhN2YwOTkwNWNjZTgM

Sample Failed Build: https://ci.chromium.org/buildbot/chromium.chromiumos/linux-chromeos-dbg/8731

Sample Failed Step: compile

Original change's description:
> [Media Session] [1/4] Move MediaMetadata to service
> 
> This CL moves the MediaMetadata and MediaImage mojo types
> from Blink to the Media Session service along with their
> mapped types in content.
> 
> This is the first of four parts.
> 
> BUG=875004
> 
> Change-Id: Ie862229bbeb474a60ccc4d2f82d8c4e1f8017b74
> Reviewed-on: https://chromium-review.googlesource.com/c/1227401
> Reviewed-by: Sadrul Chowdhury <sadrul@chromium.org>
> Reviewed-by: Daniel Cheng <dcheng@chromium.org>
> Reviewed-by: Ken Rockot <rockot@google.com>
> Commit-Queue: Becca Hughes <beccahughes@chromium.org>
> Cr-Commit-Position: refs/heads/master@{#605481}

No-Presubmit: true
No-Tree-Checks: true
No-Try: true
BUG=875004

Change-Id: Ica72191d2b5700c793fbdcf61ce680faa938f0d5
Reviewed-on: https://chromium-review.googlesource.com/c/1318747
Cr-Commit-Position: refs/heads/master@{#605520}
16 files changed