remove "historical reason" explanations

Author: tyralla

docs/source/command_line.rst

@@ -728,7 +728,7 @@ of the above sections.
        if text != b'other bytes':  # Error: non-overlapping equality check!
            ...
 
-       assert text is not None  # OK, check against None is allowed for historical reasons.
+       assert text is not None  # OK, check against None is allowed
 
 
 .. option:: --strict-equality-for-none

docs/source/error_code_list2.rst

@@ -146,7 +146,7 @@ literal:
         return x == b'magic'  # OK
 
 :option:`--strict-equality <mypy --strict-equality>` does not include comparisons with
-``None`` for historical reasons (support for type comments):
+``None``:
 
 .. code-block:: python