Fixed import problem in tests when storm-pars is not available

tests/pars/test_parametric.py

@@ -8,8 +8,6 @@ from configurations import pars
 
 @pars
 class TestParametric:
-    import stormpy.pars
-
     def test_constraints_collector(self):
         from pycarl.formula import FormulaType, Relation
         if stormpy.info.storm_ratfunc_use_cln():

tests/pars/test_pla.py

@@ -8,7 +8,6 @@ from configurations import pars
 @pars
 class TestPLA:
     def test_pla(self):
-        import stormpy.pars
         program = stormpy.parse_prism_program(get_example_path("pdtmc", "brp16_2.pm"))
         prop = "P<=0.84 [F s=5 ]"
         formulas = stormpy.parse_properties_for_prism_program(prop, program)