[documentation] Remove `--flat-videos`

It does not work as documented
It was an experimental option that I forgot to remove when making the fork public

:ci skip all

README.md

@@ -177,7 +177,6 @@ Then simply type this
                                      containing directory
     --flat-playlist                  Do not extract the videos of a playlist,
                                      only list them
-    --flat-videos                    Do not resolve the video urls
     --no-flat-playlist               Extract the videos of a playlist
     --mark-watched                   Mark videos watched (YouTube only)
     --no-mark-watched                Do not mark videos watched

youtube_dlc/options.py

@@ -201,7 +201,9 @@ def parseOpts(overrideArguments=None):
     general.add_option(
         '--flat-videos',
         action='store_true', dest='extract_flat',
-        help='Do not resolve the video urls')
+        # help='Do not resolve the video urls')
+        # doesn't work
+        help=optparse.SUPPRESS_HELP)
     general.add_option(
         '--no-flat-playlist',
         action='store_false', dest='extract_flat',