Replace update_web_docs_svn with update_web_docs_git.

This patch replaces the update_web_docs_svn script, that updates
online documentation from its sources in the GCC repository, run once
a day from cron, with update_web_docs_git.

	* update_web_docs_git: New file.
	* update_web_docs_svn: Remove.
	* crontab: Use update_web_docs_svn.