Remove unused messages from TimedText module.

See https://translatewiki.net/wiki/Thread:Support/About_MediaWiki:Mwe-timedtext-stage-upload/en
dbb9a4f4bb8c3491 and 8a15daf2da9d0697

Change-Id: I79ee0a1ede6d025602e51c60e8dc9cf2e85b5a90
Merge "Remove unused messages from TimedText module."