CLEANUP: http_ext: remove useless BUG_ON() in http_handle_xot_header()

A useless BUG_ON() statement was let in a conditional block that already
checks that the condition cannot be met within the block. Remove the
useless BUG_ON()

src/http_ext.c

@@ -870,7 +870,6 @@ int http_handle_xot_header(struct stream *s, struct channel *req)
 	}
 	if (s->be->http_ext && s->be->http_ext->xot) {
 		/* backend */
-		BUG_ON(!s->be->http_ext);
 		b_xot = s->be->http_ext->xot;
 	}