Remove mobile/compare page and references

[reemhamz]

One-line summary

The mobile compare page is out-of-date, and we've decided to remove the page alongside any references and assets

Significant changes and points to review

• Removed browsers/mobile/compare page and browsers/mobile/compare.ftl file
• Removed browsers/mobile/compare page reference in browsers/mobile
• Removed banner on firefox/browsers/compare page
• Removed assets and links leading to the page
• Redirected the browsers/mobile/compare page to browsers/mobile landing page

Issue / Bugzilla link

#14141

Testing

• http://localhost:8000/en-US/firefox/browsers/mobile/
• http://localhost:8000/en-US/firefox/browsers/compare

[alexgibson]

A couple of loose ends that can also be removed, but otherwise this looks good to me. r+wc 📞