Since PORTNAME is no longer used at the level of C code (it's only in

Since PORTNAME is no longer used at the level of C code (it's only in
Makefiles now), there's no reason for os2client to maintain its own
copy of c.h just to change #define PORTNAME.  Simplify Makefile
accordingly.  Get rid of horribly-out-of-date modified copy of c.h,
which should never have been in the distribution to start with,
since it's actually a derived file.  Now it's not needed anyway.