partial revert 676df858e984. Add back 3 messages that were really used.

When I was grepping for message usages, I assumed that all usages
of mwe-timedtext messages would be in the TimedText subdirectory
(Since after all its set up as semi its own extension, with its
own initialization files, and own message files)

That was a bad assumption. Some of the messages were used outside
that directory.

Sorry folks, my bad.

Change-Id: I7472563ebfa3bbe5cb9ebe46a5230e9574e4caaf
Follow-up: 676df858e984
(cherry picked from commit 60f809c1243d57c7a9e1831e671c28b53bd010da)