chore(ci): Remove Semgrep GHA Workflow (#872)

Semgrep is Okta's static application security testing tool. It was
previously recommended to add Semgrep directly into CI/CD pipelines or
workflows. However, the ProdSec team has enhanced the tooling, and
Semgrep scanning is now built into the platform via a GitHub
Application.

### ℹ️ Details

* You'll find all of your PRs are *already* being scanned by a dedicated
Semgrep step. Given this, you no longer need to run Semgrep via a Github
Action workflow.
* ⚠️ This PR attempts to help remove it for you. Please review
this change carefully to ensure it doesn't impact any other jobs. Any
adjustments needed to make this PR pass is the responsibility of the
owners of the repository. (You are also welcome to close this PR and
remove Semgrep CI separately).

[_Created by Sourcegraph batch change
`eduardo.boronat/Remove-Semgrep-GHA-non-EMU`._](https://sourcegraph.prod.aue1k.saasure.net/users/eduardo.boronat/batch-changes/Remove-Semgrep-GHA-non-EMU)

Author: eduardoboronat-okta