Remove error message from testErrorOutput.

Author: tyralla

mypyc/test-data/commandline.test

@@ -200,9 +200,9 @@ wtvr = next(i for i in range(10) if i == 5)
 
 d1 = {1: 2}
 
-# Make sure we can produce an error when we hit the awful None case
+# Since PR 18180, the following pattern should pose no problems anymore:
 def f(l: List[object]) -> None:
-    x = None  # E: Local variable "x" has inferred type None; add an annotation
+    x = None
     for i in l:
         if x is None:
             x = i