This reverts commit ec8afcaca5.
Explicitly enabling the warning limit causes situations
where the entire top-level documentation build fails when
a submodule documentation has warnings.
Let the CI documentation testing step enable the warning limit
instead.
Pick-to: 6.9 6.8
Fixes: QTBUG-132954
Change-Id: I8969e54073a34c3cde7059d5d5d736bfe4e509f7
Reviewed-by: Alexey Edelev <alexey.edelev@qt.io>