avformat/movenc: remove unnecessary HDR metadata log messages

avformat/movenc: remove unnecessary HDR metadata log messages

These made sense before 3ebf449766d4b69a7774c4990fb24fe71c848a3e
when the creation of these boxes was specifically requested by the
user, but now they have become unnecessary as they are just like
many other boxes: If the input has the information required, they
are written, otherwise they are not.

They were moved to verbose verbosity level (which happens to be
the last level still relatively usable), and now appear either once
(normal MP4 muxing), or thrice (with the faststart flag set) in
any normal MP4 usage, without giving much useful information. Thus,
remove them in their current form.