Remove DEBUG_QSV_TS code.
encQSVWork: check for decreasing DTS and log it if it happens.
Remove not-so-great comment.
Improve the previously removed comment.
Remove disabled code.
Cleanup ahead of improved commit.
Further cleanup.
QSV: miscellaneous timestamp-related fixes.

Disabled for now, because the out-of-order DTS we're getting in encQSVWork has bad effects which are mitigated by muxmp4 using the frame duration instead of DTS difference.