Revert "[mlir][Transforms] Dialect conversion: Skip materializations when running without converter (#101318)"
This reverts commit 2aa96fcf751ee948702e8447de62d6bea8235e3a.
This was merged without a test. Also it seems it was only fixing an
issue for users which used a particular workaround that is not actually
needed anymore (skipping UnrealizedConversionCast operands).