[libgfortran] Removing unused parts of the source code

[François-Xavier Coudert]

Hi,

* intrinsics/random.c has a Mersenne Twister code that is commented
out for many good reasons explained in the comments.

* io/format.c has commented out debugging code that might have been
useful during the heavy developement of the library, but is of no use
nowadays since 1) the format handling is, AFAICT, in a perfect shape;
2) a debugger can show all that info, and even more.

As the source is under version control, we can always get these pieces
back if we ever need it. I intend to remove them from the tree unless
someone has objections, say, in the next 48 hours.

FX