.github/workflow: remove github action workflow config

We do not use github action workflow.

Change-Id: Ibd522d1affa69151ef7d733a19a5f02d82439224
Reviewed-on: https://go-review.googlesource.com/c/pkgsite/+/787000
LUCI-TryBot-Result: golang-scoped@luci-project-accounts.iam.gserviceaccount.com <golang-scoped@luci-project-accounts.iam.gserviceaccount.com>
Reviewed-by: Neal Patel <nealpatel@google.com>
Reviewed-by: Neal Patel <neal@golang.org>
kokoro-CI: kokoro <noreply+kokoro@google.com>

.github/workflows/govulncheck.yml

diff --git a/.github/workflows/govulncheck.yml b/.github/workflows/govulncheck.yml
deleted file mode 100644
index b398390..0000000
--- a/.github/workflows/govulncheck.yml
+++ /dev/null
@@ -1,8 +0,0 @@
-name: Run govulncheck
-on: [push]
-jobs:
-  govulncheck:
-    runs-on: ubuntu-latest
-    steps:
-      - id: govulncheck
-        uses: golang/govulncheck-action@v1