qutebrowser: use yt-dlp to view video in MPV

This goes around:

ytdl-org/youtube-dl#29326

The ~/bin/qutebrowser_bin/mpv part is done through a wrapper script (in
another commit).

qutebrowser/keys.py

@@ -68,12 +68,9 @@
 # downloads
 config.bind('ed',  'download-open')
 # videos (mpv, castnow, youtube-dl)
+MPV_FLAGS="--force-window --no-terminal --keep-open=yes --ytdl --script-opts=ytdl_hook-ytdl_path=yt-dlp --ytdl-format='ytdl-format=bestvideo[height<=?1080][fps<=?30][vcodec!=?vp9]+bestaudio/best'"
 config.bind('xv',  'spawn --userscript ~/bin/qutebrowser_bin/mpv')
-
-config.bind(';xv', "hint links spawn %s {hint-url}"
-             % "mpv --force-window --no-terminal --keep-open=yes --ytdl "
-               "--ytdl-format="
-               "'ytdl-format=bestvideo[height<=?1080][fps<=?30][vcodec!=?vp9]+bestaudio/best'")
+config.bind(';xv', "hint links spawn mpv %s {hint-url}" % MPV_FLAGS)
 config.bind('xc',  'spawn --userscript ~/bin/qutebrowser_bin/cast {url}')
 config.bind(';xc', 'hint links spawn --userscript ~/bin/qutebrowser_bin/cast {hint-url}')
 ## unbinding for preventing shadowing ;Yd and ;Ym