contrib/wix/hg.cmd

util: drop write_content_size=True

This is now the default in python-zstandard 0.9. While we're here,
also add a comment about the ability to drop frame magic to save
space.

Differential Revision: https://phab.mercurial-scm.org/D3199

@echo off
rem launch hg.exe from parent folder
"%~dp0\..\hg.exe" %*