You can only delete the tag content of more than 1 file either in the tagpanel or in the extended tag view. In the tagpanel you would have to customize and add those unwanted fields, if they are not there. Because all fields are shown in the extended tag view there is no need to add fields. Just simply mark all files in the file list (CTRL-a), activate the extended tag view (ALT-t), mark 1 or more tags (pressing CTRL) in the metadata window and delete the unwanted fields with clicking on the red cross and after that o.k.
You can also do the task by an action of the type "Remove Fields" or with an action of the type "Remove fields except".