Remove the "Verify linked issue" bot

[carmocca]

What does this PR do?

Removes the "Verify linked issue" bot. The bot has too many false positives and false negatives. Some contributors have resorted to "fake" linked issues in their PRs to avoid the message spam and error mark.

We need a better solution, either by extending its implementation or finding a different bot. At the moment, the simplest option is to remove the noise.

Opens #9397
Closes #10236

Does your PR introduce any breaking changes? If yes, please list them.

None

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cc @carmocca @akihironitta @Borda

[tchaton]

LGTM !