nt/*.c, src/*.c: Remove unused variables.

nt/*.c, src/*.c: Remove unused variables.

* nt/addpm.c (main): Remove unused variable `retval'.
* nt/preprep.c (main): Remove unused variable `ptr'.
* src/dispextern.h (glyph_matric): Use #if GLYPH_DEBUG, not #ifdef.
* src/fileio.c (check_executable) [DOS_NT]: Remove unused variables `len'
  and `suffix'.
  (Fset_file_selinux_context) [HAVE_LIBSELINUX]: Move here declaration
  of variables specific to SELinux and computation of `encoded_absname'.
* src/image.c (XPutPixel): Remove unused variable `height'.
* src/keyboard.c (make_lispy_event): Remove unused variable `hpos'.
* src/unexw32.c (get_section_info): Remove unused variable `section'.
* src/w32.c (stat): Remove unused variables `drive_root' and `devtype'.
  (system_process_attributes): Remove unused variable `sess'.
  (sys_read): Remove unused variable `err'.
* src/w32fns.c (top): Wrap variables with #if GLYPH_DEBUG, not #ifdef.
  (w32_wnd_proc): Remove unused variable `isdead'.
  (unwind_create_frame): Use #if GLYPH_DEBUG, not #ifdef.
  (Fx_server_max_request_size): Remove unused variable `dpyinfo'.
  (x_create_tip_frame): Remove unused variable `tem'.
* src/w32inevt.c (w32_console_read_socket): Remove unused variable `no_events'.
* src/w32term.c (x_draw_composite_glyph_string_foreground):
  Remove unused variable `width'.