Revert "Fix white flashes"

This reverts commit 4ebeb509b7.

This commit is causing rendering errors as described in bugreport
https://bugs.kde.org/show_bug.cgi?id=426486

src/lib/webengine/webpage.cpp

@@ -81,8 +81,6 @@ WebPage::WebPage(QObject* parent)
     , m_secureStatus(false)
 {
     QWebChannel *channel = new QWebChannel(this);
-    // Prevents white flashes.
-    setBackgroundColor(MainApplication::palette().color(QPalette::Window));
     ExternalJsObject::setupWebChannel(channel, this);
     setWebChannel(channel, SafeJsWorld);