qt5_use_modules has been deprecated in 2013 (commit d9ea4bb144)
and removed for the first time in 2018, but then brought back - see
discussion in https://lists.qt-project.org/pipermail/development/2018-June/032837.html .
Anyhow, I think we can finally put it to a rest in Qt 6.
Change-Id: I770f7e93406ad68535d1d90e4a3bacfb920e2d5a
Reviewed-by: Alexandru Croitor <alexandru.croitor@qt.io>