src/*.c: Remove unused parameters and other warnings.

src/*.c: Remove unused parameters and other warnings.

* dispextern.h (string_buffer_position): Remove declaration.

* print.c (strout): Remove parameter `multibyte', unused since
  revno:25356 (1999-08-21).  All callers changed.

* search.c (boyer_moore): Remove parameters `len', `pos' and `lim',
  never used since function introduction in revno:20870 (1998-02-08).
  All callers changed.

* w32.c (_wsa_errlist): Use braces for struct initializers.

* xdisp.c (string_buffer_position_lim): Remove parameter `w',
  never used since function introduction in revno:36704 (2001-03-09).
  All callers changed.
  (string_buffer_position): Likewise.  Also, make static (it's never
  used outside xdisp.c).
  (cursor_row_p): Remove parameter `w', unused since
  revno:32591 (2000-10-17).  All callers changed.
  (decode_mode_spec): Remove parameter `precision', introduced during
  Gerd Moellmann's rewrite at revno:25013 (1999-07-21), but never used.
  All callers changed.