GRIND-45: Revert "GRIND-45: query github for the latest windows-agent build number."
This introduced a dependancy on gridcentric's environment. We will instead
create a wrapper script that passes in a valid URL for the agent to
install.
This reverts commit ca13cc0cdd0c791c180c81e7940d9d1e588e0e6f.

Change-Id: Ib39394fb03aa60a3ae3b6514ab113329c374e278