Token cache not cleared when custom date formats added or removed

[jenlampton]

Token module alters two forms in D7 (to add a submit handler that clears the token cache) that have been changed in Backdrop. These forms are system_add_date_format_type_form and system_delete_date_format_type_form.

In Backdrop, these forms have been replaced with
system_configure_date_formats_form and system_date_delete_format_form