Tiled Gallery: Remove "link to" settings and references

[SiobhyB]

Fixes #4281

Jetpack PR: Automattic/jetpack#21884

To test: Please refer to the Jetpack PR as the "central PR" with the most up-to-date testing instructions.

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PR submission checklist:

• I have considered adding unit tests where possible.
• I have considered if this change warrants user-facing release notes more info and have added them to RELEASE-NOTES.txt if necessary.

[guarani]

Tested and this change looks good except for one very minor thing: I think the horizontal line spacer needs to be removed now from the bottom of the settings sheet:

Approving now to let you make this change and merge if you agree.

[guarani]

@SiobhyB, alternatively I think it would be find to merge as-is and create a low-priority issue to follow up on this in the next phase of the project.

[peril-wordpress-mobile]

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[SiobhyB]

Thanks for the review, Paul! I went ahead to remove the bottom border in Automattic/jetpack@629704e.