emacs_strerror cleanups

emacs_strerror cleanups

* src/buffer.c, src/emacs.c, src/lread.c: Don’t include coding.h;
no longer needed, now that emacs_strerror is declared by lisp.h.
* src/coding.c (emacs_strerror): Remove; moved to emacs.c.
* src/coding.h (emacs_strerror) [emacs]: Remove decl; moved
to lisp.h.
* src/emacs.c (emacs_strerror): Move here from coding.c.  Do not
convert result string; this is now the caller’s responsibility,
as some need conversion and others don’t.
* src/fileio.c (report_file_errno, report_file_notify_error):
Use emacs_strerror rather than rolling it ourselves.
* src/lisp.h (emacs_strerror): Move decl here from coding.h.
* src/lread.c (dir_warning): Just call emacs_strerror rather than
both strerror and emacs_strerror.  Convert its result from
locale-coding-system, since it no longer does that conversion.
* src/sound.c (sound_perror):
* src/sysdep.c (emacs_perror, str_collate):
Use emacs_strerror, not strerror.