Revert "devel/py-typing-extensions: unbreak circular dependency"

Python 3.7 EOLed and removed from the tree, so this workaround is
not needed anymore.

This reverts commits 022d383b0e704ad9bdb02255c8ef0c47c52416ed and
e7a9ba1fecd9209fbb4b669ccb283cb1862c4a2a.

With hat: python