Remove non-working lgtm badges

[andreas-el]

These stopped working back in 2022. https://github.blog/2022-08-15-the-next-step-for-lgtm-com-github-code-scanning/

Resolves #1279

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Contributor checklist

• [x] :tada: This PR closes #ISSUE_NUMBER.
• [ ] :scroll: I have broken down my PR into the following tasks:
  • [ ] Task 1
  • [ ] Task 2
• [ ] :robot: I have added tests, or extended existing tests, to cover any new features or bugs fixed in this PR.
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