Block Editor: Remove CodeMirror settings.

CodeMirror is no longer used in the block editor, so we don't need to load the settings.

Merges [43857] from the 5.0 branch to trunk.

Props noisysocks.
Fixes #45248.

Built from https://develop.svn.wordpress.org/trunk@44223


git-svn-id: https://core.svn.wordpress.org/trunk@44053 1a063a9b-81f0-0310-95a4-ce76da25c4cd