It doesn't make sense to build any tooling or plugins for the importing
of assets on non-development platforms. This tooling is not intended to
be used at runtime, so don't even bother building it.

Fixes: QTBUG-80572
Change-Id: I442a82df6d299fdd13d9c02faeaeace3f2553e7c
Reviewed-by: Inho Lee <inho.lee@qt.io>
Reviewed-by: Christian Strømme <christian.stromme@qt.io>