Remote unused cruft file (#1112)

In 8e7147f4, it seems that proxy/assert_macro was committed erroneously.

This change removes this unused file.

proxy/assert_macro

@@ -1,29 +0,0 @@
-
-macro_rules! assert_metrics {
-    (
-        $metrics:ident,
-        $label_1:ident = $value_1:ident,
-        $($label_n:ident = $value_n:ident),*
-        => $($rest:tt)+
-    ) => {
-        assert_metrics!(@inner $metrics,
-            concat!(
-                stringify!($label_1), "=\"", stringify!($value_1), "\"",
-                $(",", stringify!($label_n), "=\"", stringify!($value_n), "\""),*,
-            ) => $($rest)+
-        );
-    };
-    (@inner $metrics:ident, $labels:expr =>
-     $($metric_name:ident = $metric_value:expr),+) => {
-        $(
-            assert_contains!(
-                $metrics.get("/metrics"),
-                concat!(
-                    stringify!($metric_name),
-                    "{", $labels, "} ",
-                    stringify!($metric_value)
-                )
-            );
-        )+
-    };
-}