[lldb/tests] Removed add_test_categories decorator for python API tests, NFC

There is a .categories file in the python_api directory that makes all nested tests
belong to the category "pyapi". The decorator is unnecessary for these tests.

lldb/test/API/python_api/sbvalue_persist/TestSBValuePersist.py

@@ -13,7 +13,6 @@ class SBValuePersistTestCase(TestBase):
     mydir = TestBase.compute_mydir(__file__)
     NO_DEBUG_INFO_TESTCASE = True
 
-    @add_test_categories(['pyapi'])
     @expectedFailureAll(oslist=["windows"], bugnumber="llvm.org/pr24772")
     def test(self):
         """Test SBValue::Persist"""