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-script.c

@@ -501,7 +501,7 @@ print_command_trace (const char *fmt, ...)
   va_list args;
 
   va_start (args, fmt);
-  vprintf_filtered (fmt, args);
+  gdb_vprintf (fmt, args);
   va_end (args);
   puts_filtered ("\n");
 }