Deployment doc still mentions hardcoded prefix path in Qt5Core.dll

Hi, one very welcome improvement in 5.14.0 was the removal of the hardcoded qt_prfxpath in QtCore.dll (for more see https://bugreports.qt.io/browse/QTBUG-14150)

However the documentation needs to be updated as well, for example, the paragraphs at the bottom of https://doc.qt.io/qt-5.14/windows-deployment.html ( qtdoc\doc\src\platforms\windows.qdoc:1055 ) still mention how to workaround problems when the hardcoded qt_prfxpath ".. does not exist on the target machine.." (And the advice to "... Using a third party installation utility ..", i.e. windeployqt.exe, to reset the qt_prfxpath in Qt5Core.dll to "." is also irrelevant now with 5.14.0)