Remove reference to --with-python3.

configure.ac

@@ -82,7 +82,7 @@ dnl and programs.
 AC_CHECK_PROGS([PYTHON], [python3], [none])
 AS_IF([test "x$PYTHON" = xnone],
 	    [AC_MSG_FAILURE(
-		[--with-python3 given but no acceptable python3 could be found])])
+		[No acceptable python3 could be found])])
 
 dnl----
 dnl With the following set of macros, we implement an option 

guix-env.scm

@@ -44,7 +44,7 @@
 ;;;   git submodule init
 ;;;   git submodule update
 ;;;   ./bootstrap.sh
-;;;   ./configure --with-python3 --without-virtualenv
+;;;   ./configure --without-virtualenv
 ;;;   make
 ;;;   python3 -m venv --system-site-packages . && bin/python setup.py develop  --no-deps
 ;;;   bin/python -m pip install --force-reinstall PasteScript # workaround