Editor: Remove unwanted fields before saving posts.

The meta_input, file, and guid fields are not intended to be updated through user input.

Merges [44047] to trunk.
Built from https://develop.svn.wordpress.org/trunk@44295


git-svn-id: https://core.svn.wordpress.org/trunk@44125 1a063a9b-81f0-0310-95a4-ce76da25c4cd