Remove -N option (--skip-numeric-underscore-normalization) from black

The option used to preserve underscores in numeric literals
has been removed from Black.

Black no longer normalizes numeric literals to include _ separators.

See:
psf/black#549
psf/black#696
Signed-off-by: Enrico Usai <usai@amazon.com>

cli/tox.ini

@@ -43,7 +43,7 @@ skip_install = true
 deps =
     black
 commands =
-    black -l 120 -N  \
+    black -l 120 \
         {[vars]code_dirs} \
         {posargs}