Upgrade MediaElement to 2.15.1.

Changes from 2.15.0:
https://github.com/johndyer/mediaelement/compare/2.15.0...2.15.1

Continues to revert upstream commit b7f82b4 to restore the status quo for Chromium support.

See [29688].
Fixes #29620 for trunk.

Built from https://develop.svn.wordpress.org/trunk@29733


git-svn-id: http://core.svn.wordpress.org/trunk@29507 1a063a9b-81f0-0310-95a4-ce76da25c4cd