Tidyup: Remove unused `Display.novideo` member
Tidyup: Remove unused `Display.novideo` member

It was introduced in aee8f04d9 "stbt.Display.teardown doesn't hang when No
Video", but it's been unused since 75de4f499 "Tear down the sink pipeline
even if `NoVideo`".  The latter seems to be an incomplete reversion of the
former.

stb-tester/stb-tester,stb-tester/stb-tester,stb-tester/stb-tester,stb-tester/stb-tester