Site Health: Move `post_max_size` and `upload_max_filesize` out of a...

Site Health: Move `post_max_size` and `upload_max_filesize` out of a translatable string in file upload checks.

Simplify some other strings, use a consistent format for translator comments.

Follow-up to [48535].

See #50038.
Built from https://develop.svn.wordpress.org/trunk@48539


git-svn-id: https://core.svn.wordpress.org/trunk@48301 1a063a9b-81f0-0310-95a4-ce76da25c4cd