JSHint removed from CodeMirror in 4.9.3

CodeMirror was introduced to WordPress 4.9 for an improved code editing experience. For JavaScript linting, CodeMirror uses JSHint which unfortunately includes some code that isn't compatible with the GPL. Therefore, in WordPress 4.9.3, we are removing JSHint and replacing it with esprima and a custom wrapper to provide some basic linting for JavaScript. This allows the code editor to show compilation errors, but not errors in formatting. 

If your code relies upon JSHint from core, you should update that code to include a copy of JSHint.  Please note that as JSHint isn't currently GPL compatible, it can not be distributed in the WordPress Plugin Repository. 

For more info, please see #42850.

#4-9, #4-9-3, #codemirror, #dev-notes, #jshint