[metrics] Delete test that doesn't make sense

This test is ignored because we expect it to "ignore but fail".

But it will generate a fatal error because it doesn't have the
metrics file, thus should have been skipped instead.

metrics/tests/probes/file-size/fail-file-not-found/style.json

@@ -1,32 +0,0 @@
-{
-  "version": 8,
-  "metadata": {
-    "test": {
-      "operations": [
-        ["probeFileSize", "style", "style.aaaa", 0],
-        ["probeFileSize", "image", "expected.bbb", 0]
-      ],
-      "width": 64,
-      "height": 64
-    }
-  },
-  "sources": {
-    "geojson": {
-      "type": "geojson",
-      "data": {
-        "type": "Point",
-        "coordinates": [
-          0,
-          0
-        ]
-      }
-    }
-  },
-  "layers": [
-    {
-      "id": "circle",
-      "type": "circle",
-      "source": "geojson"
-    }
-  ]
-}