py/objstr: Split mp_obj_str_from_vstr into bytes/str versions.

Previously the desired output type was specified.  Now make the type part
of the function name.  Because this function is used in a few places this
saves code size due to smaller call-site.

This makes `mp_obj_new_str_type_from_vstr` a private function of objstr.c
(which is almost the only place where the output type isn't a compile-time
constant).

This saves ~140 bytes on PYBV11.

Signed-off-by: Jim Mussared <jim.mussared@gmail.com>

py/parsenum.c

@@ -160,7 +160,7 @@ value_error:
         mp_printf(&print, "invalid syntax for integer with base %d: ", base);
         mp_str_print_quoted(&print, str_val_start, top - str_val_start, true);
         mp_obj_t exc = mp_obj_new_exception_arg1(&mp_type_ValueError,
-            mp_obj_new_str_from_vstr(&mp_type_str, &vstr));
+            mp_obj_new_str_from_vstr(&vstr));
         raise_exc(exc, lex);
         #endif
     }