Remove support for DJGPP v1.x (bug#5813).

Remove support for DJGPP v1.x (bug#5813).

 src/:
 w16select.c (__dpmi_int): Remove DJGPP v1.x compatibility.
 s/msdos.h:
 unexec.c (make_hdr, copy_text_and_data):
 sysdep.c (wait_for_termination, sys_subshell):
 msdos.c (dos_set_window_size, msdos_set_cursor_shape)
 (IT_set_terminal_modes):
 (__write, _rename, gethostname, gettimeofday, alarm, fork, kill)
 (dos_ttraw, dos_ttcooked, run_msdos_command, abort): Remove DJGPP
 v1.x code and tests of the value of __DJGPP__.
 (nice, pause, sigsetmask, sigblock): Remove DJGPP v1.x
 compatibility code.
 lread.c:
 gmalloc.c (memalign):
 fileio.c (Fcopy_file, check_executable, Ffile_modes):
 emacs.c (main):
 dosfns.c (init_dosfns):
 dired.c (file_name_completion_stat): Remove tests of __DJGPP__.

 msdos/:
 sed3.inp:
 sed2.inp:
 sed1.inp:
 mainmake: Files removed.