py/makemoduledefs.py: Remove shebang line and adjust style of comment.

This file is not executable so shouldn't have the shebang line.  This line
can cause issues when building on Windows msvc when the PyPython variable
is set to something other than "python", because it reverts back to using
the shebang line.

The top comment is also changed to """ style which matches all other
preprocessing scripts in the py/ directory.
Signed-off-by: Damien George <damien@micropython.org>

py/makemoduledefs.py

-#!/usr/bin/env python
-
-# This pre-processor parses a single file containing a list of
-# MP_REGISTER_MODULE(module_name, obj_module)
-# These are used to generate a header with the required entries for
-# "mp_rom_map_elem_t mp_builtin_module_table[]" in py/objmodule.c
+"""
+This pre-processor parses a single file containing a list of
+MP_REGISTER_MODULE(module_name, obj_module)
+These are used to generate a header with the required entries for
+"mp_rom_map_elem_t mp_builtin_module_table[]" in py/objmodule.c
+"""
 
 from __future__ import print_function