removed obsolete THIS_IS_ISABELLE_BUILD/MAKEBIN feature;

--- a/Admin/makebin	Wed Mar 05 22:58:13 2008 +0100
+++ b/Admin/makebin	Thu Mar 06 19:21:19 2008 +0100
@@ -12,9 +12,6 @@
 TAR=tar
 type -path gtar >/dev/null && TAR=gtar
 
-export THIS_IS_ISABELLE_BUILD=true
-export THIS_IS_ISABELLE_MAKEBIN=true
-
 
 ## diagnostics