Revert "Let people know they need to export MONO_VERSION."
Revert "Let people know they need to export MONO_VERSION."

This reverts commit 6140b6b133b9afa82ba0eea9628df2f18fe348cc.
This check was not sufficient. I put this check inside the actual
mono-master.py file so that any profile which tries to build mono
will correctly fail when MONO_VERSION is missing.

mono/bockbuild,mono/bockbuild