Remove DOS/DJGPP support

DJGPP is a port of the GNU toolchain to 32-bit x86 systems running DOS.
The last known attempt to build Perl on it was on 5.20, which only got
as far as building miniperl.

MANIFEST

@@ -4131,12 +4131,6 @@ dist/Unicode-Normalize/t/tie.t		Unicode::Normalize
 dist/XSLoader/Makefile.PL	Dynamic Loader makefile writer
 dist/XSLoader/t/XSLoader.t	See if XSLoader works
 dist/XSLoader/XSLoader_pm.PL	Simple XS Loader perl module
-djgpp/config.over	DOS/DJGPP port
-djgpp/configure.bat	DOS/DJGPP port
-djgpp/djgpp.c		DOS/DJGPP port
-djgpp/djgpp.h		DOS/DJGPP port
-djgpp/djgppsed.sh	DOS/DJGPP port
-djgpp/fixpmain		DOS/DJGPP port
 doio.c			I/O operations
 doop.c			Support code for various operations
 dosish.h		Some defines for MS/DOSish machines
@@ -4693,7 +4687,6 @@ hints/cygwin.sh			Hints for named architecture
 hints/darwin.sh			Hints for named architecture
 hints/dcosx.sh			Hints for named architecture
 hints/dec_osf.sh		Hints for named architecture
-hints/dos_djgpp.sh		Hints for named architecture
 hints/dragonfly.sh		Hints for named architecture
 hints/dynix.sh			Hints for named architecture
 hints/dynixptx.sh		Hints for named architecture
@@ -5441,7 +5434,6 @@ README.android			Perl notes for Android
 README.bs2000			Perl notes for POSIX-BC BS2000
 README.cn			Perl for Simplified Chinese (in UTF-8)
 README.cygwin			Perl notes for Cygwin
-README.dos			Perl notes for DOS
 README.freebsd			Perl notes for FreeBSD
 README.haiku			Perl notes for Haiku
 README.hpux			Perl notes for HP-UX

Porting/pumpkin.pod

@@ -191,7 +191,7 @@ If you have many machine-specific #defines or #includes, consider
 creating an "osish.h" (F<os2ish.h>, F<vmsish.h>, and so on) and including
 that in F<perl.h>.  If you have several machine-specific files (function
 emulations, function stubs, build utility wrappers) you may create a
-separate subdirectory (djgpp, win32) and put the files in there.
+separate subdirectory (vms, win32) and put the files in there.
 Remember to update C<MANIFEST> when you add files.
 
 If your system supports dynamic loading but none of the existing