Remove mozilla_monitor conditionals (Fixes #14493)

[alexgibson]

One-line summary

Removed the conditional since Mozilla Monitor has been out for quite some time now, and it's time to retire any of the old and obsolete Firefox Monitor strings and references.

Sibling PR for switch: mozmeao/www-config#560

Significant changes and points to review

• Removed conditionals from relevant HTML files
• Removed obsolete Firefox Monitor strings from relative Fluent files

Issue / Bugzilla link

Fixes #14492
Supersedes #14493

Testing

• http://localhost:8000/en-US/account/
• http://localhost:8000/en-US/firefox/welcome/1/
• http://localhost:8000/en-US/firefox/welcome/7
• http://localhost:8000/en-US/firefox/welcome/8
• http://localhost:8000/en-US/privacy/products/
• http://localhost:8000/en-US/products/
• http://localhost:8000/en-US/firefox/privacy/safe-passwords/
• http://localhost:8000/en-US/firefox/browsers/best-browser/
• http://localhost:8000/en-US/firefox/privacy/book/

[alexgibson]

Note that this PR is still missing some changes from the original PR that will need manually adding here, as they were accidentally squashed into a commit from another PR.

[reemhamz]

Thanks so much Alex!! You're a git-king 👑 I pushed some changes that should cover the missing files. Let me know if I missed anything.

[alexgibson]

I took a look through the updates and they look OK to me - but I can't approve the PR since I opened it. Perhaps either @craigcook or @stephaniehobson can do the honors?

I'm really glad you managed to save things OK!

[reemhamz]

Spoke w/ Alex and agreed that since he approved these same changes in the previous PR, then this is okay for me to approve and merge 👍🏼 Thanks again Alex!