Remove mechanism for setting $GOPATH in /etc/profile.d

Setting $GOPATH via /etc/profile.d proved difficult to work around in a
CI environment. For development, the default of $GOPATH == $HOME
automatically adds $HOME/bin to $PATH, which is desirable.
Merge pull request #1 from azavea/feature/hmc/remove-profile.d

Remove mechanism for setting $GOPATH in /etc/profile.d