[qtdeclarative] Do not build dialogs.

These are moved to QtQuickControls and no longer part of
QtQuick core upstream.

Change-Id: Icbb29833d7b0365dc6a13c94239e34b0551a4fc7
[qtdeclarative] Packaging: don't package dialogs

Change-Id: I040dd928353c2d251b192ca9711d6419b19af00f