Revert "gnu: kwayland: Enable test suite."

This reverts commit ba3e25bb.

This commit is reverted because it caused kwayland to no longer build on the
build farm. Specifically, the test "PlasmaWindowModelTest::testVirtualDesktops"
fails.

See this discussion for more information:

https://lists.gnu.org/archive/html/guix-devel/2021-01/msg00382.html