Revert "Qt Designer: Temporarily disable loading of QDeclarativeView plugin."

This reverts commit 8334921061a3e4cfc5ce08e5a837564d40f70714.

The issue has been fixed in Qt.

Task-number: QTCREATORBUG-10273
Task-number: QTBUG-35006
Change-Id: I8891e5c7821f89e9a83442685b2833fa6a0de10e
Reviewed-by: Simon Hausmann <simon.hausmann@digia.com>