commands/new: Remove format flag from new content cmd

Fixes #11462

content/en/commands/hugo_new_content.md

@@ -30,7 +30,6 @@ hugo new content [path] [flags]
   -c, --contentDir string   filesystem path to content directory
       --editor string       edit new content with this editor, if provided
   -f, --force               overwrite file if it already exists
-      --format string       preferred file format (toml, yaml or json) (default "toml")
   -h, --help                help for content
   -k, --kind string         content type to create
   -t, --theme strings       themes to use (located in /themes/THEMENAME/)