ocamlPackages_3_11_2: remove

This requires removing also the Coq 8.3 and Matita 0.5.8 packages.

Coq 8.3 was released 8 years ago (2010) and there is no trace left
of users of this version (contrary to Coq 8.4, released 2012).
It is well over time to remove it.

Matita 0.5.8 was released in 2010 and because this version was still
used for teaching according to the official website, a legacy release
(0.5.9) was released in 5 years later to compile with more recent
OCaml libraries.
Updating to 0.5.9 (or a more recent version like 0.99.3) should allow
getting rid of the dependency on older OCaml but it is hard to test
given that the package is already broken before this update.