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/exceptions.c

@@ -127,7 +127,7 @@ exception_fprintf (struct ui_file *file, const struct gdb_exception &e,
 
       /* Print the prefix.  */
       va_start (args, prefix);
-      vfprintf_filtered (file, prefix, args);
+      gdb_vprintf (file, prefix, args);
       va_end (args);
 
       print_exception (file, e);