Fix a padding issue with the new CodeMirror CSS.
Fix a padding issue with the new CodeMirror CSS.

The updated CodeMirror CSS file introduced some new padding at the
beginning of lines, which we don't want to include. This turns it off in
favor of the padding we've already set.

chipx86/reviewboard,chipx86/reviewboard,reviewboard/reviewboard,reviewboard/reviewboard,chipx86/reviewboard,chipx86/reviewboard,reviewboard/reviewboard,reviewboard/reviewboard