[Qt] Remove setDeviceSize methods

[Qt] Remove setDeviceSize methods

https://bugs.webkit.org/show_bug.cgi?id=46347

Reviewed by Antonio Gomes.

Remove our setDeviceHeight() API and obtain it automatically from the
system. Also for testing purposes, make it possible to override the
values via two newly introduced environment variables.

* Api/qgraphicswebview.cpp:
* Api/qgraphicswebview.h:
* Api/qwebpage.cpp:
(getintenv):
(queryDeviceSizeForScreenContainingWidget):
(QWebPage::viewportConfigurationForSize):
* WebCoreSupport/PageClientQt.cpp:
(WebCore::PageClientQGraphicsWidget::windowRect):
* symbian/eabi/QtWebKitu.def:

git-svn-id: http://svn.webkit.org/repository/webkit/trunk@68457 268f45cc-cd09-0410-ab3c-d52691b4dbfc