Removal of dead code, and explicit Python version dispatch (#13984)

This should remove dead code and make explicit version testing

IPython/core/tests/test_oinspect.py

@@ -514,28 +514,20 b' def test_render_signature_long():'
         signature(long_function),
         long_function.__name__,
     )
-    assert sig in [
-        # Python >=3.9
-        '''\
+    if sys.version_info >= (3, 9):
+        expected = """\
 long_function(
     a_really_long_parameter: int,
     and_another_long_one: bool = False,
     let_us_make_sure_this_is_looong: Optional[str] = None,
 ) -> bool\
-''',
-        # Python >=3.7
-        '''\
+"""
+    else:
+        expected = """\
 long_function(
     a_really_long_parameter: int,
     and_another_long_one: bool = False,
     let_us_make_sure_this_is_looong: Union[str, NoneType] = None,
 ) -> bool\
-''',  # Python <=3.6
-        '''\
-long_function(
-    a_really_long_parameter:int,
-    and_another_long_one:bool=False,
-    let_us_make_sure_this_is_looong:Union[str, NoneType]=None,
-) -> bool\
-''',
-    ]
+"""
+    assert sig == expected