In commit aa002f5c6d, a handlebars template was created for empty
narrow feed messages, which removed a number of div element ids,
and updated `narrow_banner.show_empty_narrow_message` to first
empty the main empty narrow div of any previous message content.
Removes the helper function for hiding the empty narrow messages
as `narrow_banner.show_empty_narrow_message` should empty the
empty message div of any text before rendering the updated empty
narrow for the new empty narrow banner text.
Also, cleans up a missed instance of 'uri' from commit b22578f
in the same test.
982a37aece