[test] Fix apple_simulator_test decorator when simulators are unavailable

In the case where xcodebuild fails as you set up simulator tests, you
would fail because `feature` is never defined.

lldb/packages/Python/lldbsuite/test/decorators.py

@@ -364,7 +364,7 @@ def apple_simulator_test(platform):
             else:
                 return "%s simulator is not supported on this system." % platform
         except subprocess.CalledProcessError:
-            return "%s is not supported on this system (xcodebuild failed)." % feature
+            return "Simulators are unsupported on this system (xcodebuild failed)"
 
     return skipTestIfFn(should_skip_simulator_test)