Unify vprintf functions

Now that filtered and unfiltered output can be treated identically, we
can unify the vprintf family of functions: vprintf_filtered,
vprintf_unfiltered, vfprintf_filtered and vfprintf_unfiltered.  (For
the gdb_stdout variants, recall that only printf_unfiltered gets truly
unfiltered output at this point.)  This removes one such function and
renames the remaining two to "gdb_vprintf".  All callers are updated.
Much of this patch was written by script.

gdb/cli/cli-cmds.c

@@ -2038,7 +2038,7 @@ ambiguous_line_spec (gdb::array_view<const symtab_and_line> sals,
 {
   va_list ap;
   va_start (ap, format);
-  vprintf_filtered (format, ap);
+  gdb_vprintf (format, ap);
   va_end (ap);
 
   for (const auto &sal : sals)