Remove dmpstruct.h

Remove dmpstruct.h

The hassles of updating the dmpstruct.h-using code bit me again.
These updates are more trouble than they’re worth.  See:
https://lists.gnu.org/r/emacs-devel/2019-03/msg00122.html
As I’m the main person who’s made changes in this area since
dmpstruct.h was introduced, I’m the most motivated to clean up
the situation.
* make-dist (possibly_non_vc_files): Remove src/dmpstruct.h.
* src/Makefile.in (dmpstruct_headers, dmpstruct.h): Remove.
(pdumper.o): Do not depend on dmpstruct.h.
(mostlyclean): Do not remove dmpstruct.h.
* src/dmpstruct.awk: Remove.
* src/pdumper.c: Do not include dmpstruct.h.
(CHECK_STRUCTS): Remove.  All uses removed.