tiny code cleanup

kwant/__init__.py

@@ -16,11 +16,11 @@ from .builder import Builder
 __all__.append('Builder')
 
 from .lattice import TranslationalSymmetry
-__all__.extend(['TranslationalSymmetry'])
+__all__.append('TranslationalSymmetry')
 
 # Make kwant.solvers.default.solve available as kwant.solve.
 solve = solvers.default.solve
-__all__.extend(['solvers', 'solve'])
+__all__.append('solve')
 
 # Importing plotter might not work, but this does not have to be a problem --
 # only no plotting will be available.