Fixes RST link formatting.
Unfortunately, "source formatted" links like
see [`optax`](https://optax.readthedocs.io/)
are not supported in RST:
- https://github.com/spatialaudio/nbsphinx/issues/301
- https://docutils.sourceforge.io/FAQ.html#is-nested-inline-markup-possible
So removing the "source formatting" so these links render as normal text (but
with correct link formatting) in both Colab and RTD.
