Update METADATA to link to upstream project am: 2e54c35cfe am: 68d5fa8757

Original change: https://android-review.googlesource.com/c/platform/external/libmpeg2/+/2475549

Change-Id: I731b180d01b366c5dfa55c44c51add75be6872c8
Signed-off-by: Automerger Merge Worker <android-build-automerger-merge-worker@system.gserviceaccount.com>