metrics: Remove vendor directory

PR #12892 fully removed the metrics test workflow but it
missed the editorconfig check.

Signed-off-by: Greg Kurz <groug@kaod.org>

.editorconfig-checker.json

@@ -7,7 +7,6 @@
   "Exclude": [
     "src/runtime/vendor",
     "src/tools/log-parser/vendor",
-    "tests/metrics/cmd/checkmetrics/vendor",
     "src/runtime/virtcontainers/pkg/cloud-hypervisor/client",
     "\\.img$",
     "\\.dtb$",