bpo-34838: Use subclass_of for math.dist. (GH-9659)

Argument clinic now generates fast inline code for
positional parsing, so the manually implemented type
check in math.dist can be removed.
diff --git a/Modules/clinic/mathmodule.c.h b/Modules/clinic/mathmodule.c.h
index 1c8fc2f..82a4c4a 100644
--- a/Modules/clinic/mathmodule.c.h
+++ b/Modules/clinic/mathmodule.c.h
@@ -310,7 +310,15 @@
     if (!_PyArg_CheckPositional("dist", nargs, 2, 2)) {
         goto exit;
     }
+    if (!PyTuple_Check(args[0])) {
+        _PyArg_BadArgument("dist", 1, "tuple", args[0]);
+        goto exit;
+    }
     p = args[0];
+    if (!PyTuple_Check(args[1])) {
+        _PyArg_BadArgument("dist", 2, "tuple", args[1]);
+        goto exit;
+    }
     q = args[1];
     return_value = math_dist_impl(module, p, q);
 
@@ -548,4 +556,4 @@
 exit:
     return return_value;
 }
-/*[clinic end generated code: output=f3264ab0ef57ba0a input=a9049054013a1b77]*/
+/*[clinic end generated code: output=0664f30046da09fe input=a9049054013a1b77]*/