Replace usge of long deprecated and removed wfSuppressWarnings and wfRestoreWarnings

[kghbln]

@paladox @Hutchy68 So this definitively broke compat with MediaWiki 1.31.x LTS and earlier. It will be great to know if MW 1.32.x and MW 1.34.x for me being able to update the docu.

This is yet another utterly ridiculous situation where it is not possible to support MediaWiki from one LTS to the next one without extra effort.

Setup

• MediaWiki | 1.31.6 (c168a3f)13:28, 19 December 2019
• PHP | 7.0.33-0+deb9u6 (apache2handler)
• MariaDB | 10.1.41-MariaDB-0+deb9u1
• Foreground 2.2.3

Issue

Fatal error: Uncaught Error: Class 'Wikimedia\AtEase\AtEase' not found in /../w/skins/foreground/Foreground.skin.php:63

Stack trace

#0 /../w/includes/skins/SkinTemplate.php(251): foregroundTemplate->execute()
#1 /../w/includes/OutputPage.php(2388): SkinTemplate->outputPage()
#2 /../w/includes/exception/MWExceptionRenderer.php(137): OutputPage->output()
#3 /../w/includes/exception/MWExceptionRenderer.php(54): MWExceptionRenderer::reportHTML(Object(Error))
#4 /../w/includes/exception/MWExceptionHandler.php(75): MWExceptionRenderer::output(Object(Error), 2)
#5 /../w/includes/exception/MWExceptionHandler.php(149): MWExceptionHandler::report(Object(Error))
#6 /../w/includes/exception/MWExceptionHandler.php(121): MWExceptionHandler::handleException(Object(Error))
#7 [internal function]: MWExceptionHandler::handleUncaughtException(Object(Error))
#8 {main} throw in /../w/skins/foreground/Foreground.skin.php on line 63