Deprecate MediaError.MEDIA_ERR_ENCRYPTED

Intent to Deprecate:
https://groups.google.com/a/chromium.org/d/msg/blink-dev/C3h1LApSVx8/G2s2OV5azvgJ

BUG=none

Review URL: https://codereview.chromium.org/132903015

git-svn-id: svn://svn.chromium.org/blink/trunk@166206 bbb929c8-8fbe-4397-9dbb-9b2b20218538