Remove message getShareFeedbackLink while message handler is not ready

[franfaccin]

Reviewer:

Description:

We were requesting the Feedback Form url through a message getShareFeedbackLink, but since this message handler is not ready yet, it was throwing errors in the background.

Steps to test this PR:

Build steps: https://github.com/duckduckgo/duckduckgo-privacy-extension/blob/develop/CONTRIBUTING.md#building-the-extension

1. Access https://privacy-test-pages.glitch.me/privacy-protections/youtube-click-to-load/2.
2. Inspect background page
3. It should not throw an error Unrecognized message to background: {messageType: 'getShareFeedbackLink', options: ''}

Automated tests:

• Unit tests
• Integration tests

Reviewer Checklist:

• Ensure the PR solves the problem
• Review every line of code
• Ensure the PR does no harm by testing the changes thoroughly
• Get help if you're uncomfortable with any of the above!
• Determine if there are any quick wins that improve the implementation

PR Author Checklist:

• Get advice or leverage existing code
• Agree on technical approach with reviewer (if the changes are nuanced)
• Ensure that there is a testing strategy (and documented non-automated tests)
• Ensure there is a documented monitoring strategy (if necessary)
• Consider systems implications