continuum: remove some names from the API for now

kwant/continuum/__init__.py

@@ -12,13 +12,12 @@ from .._common import ExtensionUnavailable
 
 try:
     from .discretizer import discretize, discretize_symbolic, build_discretized
+    from ._common import sympify, lambdify
     from ._common import momentum_operators, position_operators
-    from ._common import sympify, lambdify, make_commutative
 except ImportError:
     sys.modules[__name__] = ExtensionUnavailable(__name__, ('sympy',))
 
 del sys, ExtensionUnavailable
 
 __all__ = ['discretize', 'discretize_symbolic', 'build_discretized',
-           'momentum_operators', 'position_operators', 'sympify',
-           'lambdify', 'make_commutative']
+           'sympify', 'lambdify']