Revert "BLD-642: Allow multiple transcripts with video." (BLD-899)

This reverts commit 25407ef3e73ab947114256c53d2e6ff264c99dd0.

Conflicts:
	cms/djangoapps/contentstore/transcripts_utils.py
	common/lib/xmodule/xmodule/video_module.py
	lms/envs/common.py