mw: Remove 'Report problem' feature

Removed the "report" slide from the mw.ViewPageTarget save
dialog and everything that becomes obsolete as a result of it:

* JS saveDialogReviewWrongButton, which pointed to the report
     slide (was already hidden as of I90de95f6337ee).
* JS ve.init.mw.Target#reportProblem.
* JS ve.init.mw.ViewPageTarget#diffHtml.
* JS ve.dm.ElementLinearData#getUsedStoreValues.
* PHP mw.config wgVisualEditorConfig.reportProblemURL.
* PHP $wgVisualEditorParsoidProblemReportURL.
* I18N visualeditor-savedialog-title-report.
* I18N visualeditor-savedialog-label-review-wrong

Change-Id: I8a5e0ab2060d7c14086bba413d4c7d73b29c9b97
Merge "mw: Remove 'Report problem' feature"