Revert "regen/regcharclass.pl: Make more EBCDIC-friendly"

This reverts commit c4c8e61502fd5289a080f20332c6e3f9f23ce6e2.

It turns out that this scheme to bootstrap regcharclass.h onto a machine
not running ASCII created too much manual labor getting things to work.
A better solution is to cross compile on an ASCII machine for the
target.  Commit 6ff677df5d6fe0f52ca0b6736f8b5a46ac402943 created the
infrastructure to do that, and this commit starts the process of
changing regen/regcharclass.pl to use that.