[rn] enabled disableLegacyMode everywhere (#34947)

Stacked on https://github.com/facebook/react/pull/34946

This should be a noop, now that the legacy renderers are not being
sync'd.

DiffTrain build for [dd53a946ecf4805ea0ecb885e538f69e8e3cbd61](https://github.com/facebook/react/commit/dd53a946ecf4805ea0ecb885e538f69e8e3cbd61)