Log Message:
tex-platex{,-doc}: update to 2021

* More fix of \fontshape etc to work fine with LaTeX2e 2021-06-01.
* Fix an error with rolling back with the platexrelease package.

Provides a format `pLaTeX2e <2021-06-01>`,
aiming to synchronize with `LaTeX2e <2021-06-01>`.