Since the "Plain Text" format can't be deleted (within /admin/config/content/formats) the Text format pull-down will always contain it plus the default format that you would like for the user to use (i.e. Full HTML) when creating content.
When the user creates content (i.e. /node/add/article) I would like the "Text format" pull-down to be disabled so that they can't change it for non-administrators.
How can I disable the "Text format" pull-down for users that are creating or editing content?