Remove Manjaro from recommended distributions list

It pains me to submit this merge request, but I think it would be in our users' interest to no longer recommend Manjaro on the distributions page, for the following reasons:

• Its Plasma spin is quite neglected and suffers from unnecessary errors such as an old theme forked from Breeze which has not been updated in ages, and additions to System Settings which introduce redundancy and UX problems. We have received many bug reports related to these issues.
• Its SSL certificates have expired twice in recent years, and the recommended user workaround to change the system time was completely inappropriate.
• Its packaging and engineering quality are questionable, and updates have broken users' systems multiple times in recent memory, due partially to shipping an AUR installer helper which conceptually conflicts with the decision to delay packages.
• Governance was called into question over a controversy with the treasurer being dismissed after an audit.
• As an Arch-based distro, it does not ship debug symbols, so crash reports we get from users are mostly a useless waste of everyone's time.