remove semgrep gh action (#337)

## Description
We are doing this with Semgrep Cloud now.
<!-- description here -->

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## Checklist

<!--
Kubernetes, both Kustomize and Helm, and Docker Compose MUST be kept in
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You should not merge a change here without a corresponding change in the
other repositories,
unless it is specific to this deployment type. If uneeded, add link or
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- [x] Update
[CHANGELOG.md](https://github.com/sourcegraph/deploy-sourcegraph-k8s/blob/main/CHANGELOG.md)
- [x] Update [K8s Upgrade
notes](https://github.com/sourcegraph/sourcegraph/blob/main/doc/admin/updates/kubernetes.md)
- [x] Kustomiz-specific changes
- [x] Update sister repository:
[deploy-sourcegraph-helm](https://github.com/sourcegraph/deploy-sourcegraph-helm)
- [x] Update sister repository:
[deploy-sourcegraph-docker](https://github.com/sourcegraph/deploy-sourcegraph-docker)
- [x] Verify all images have a valid tag and SHA256 sum

## Test plan
n/a
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are REQUIRED to
provide a "test plan". A test plan is a loose explanation of what you
have done or
implemented to test this, as outlined in our Testing principles and
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https://docs.sourcegraph.com/dev/background-information/testing_principles
  Write your test plan here after the "Test plan" header.
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Author: andreeleuterio