Trying to delete a Custom Field, it's empty for all assets and unassigned from all Fieldsets. Get "405 Method Not Allowed" error instead.
Checked Handler Mappings for this websites PHP on the server and it has GET,HEAD,POST,DELETE,PUT,PATCH already set. I did try it with all verbs allowed and that made no difference.
Currently using version v8.2.2-pre - build 19319 (master)