signingscript: make black and flake8 happy

Once upon a time black and pydocstyle disagreed on blank lines before
nested functions, and a comment would appease them both.
Since then, the latter has been changed to not complain about a blank
line (PyCQA/pydocstyle#426), and the former now
complains about the missing blank line even with the comment
(psf/black#3302).

signingscript/src/signingscript/sign.py

@@ -87,7 +87,7 @@ def get_rss():
 
 def time_async_function(f):
     """Time an async function."""
-    # comment to keep black/flake8 happy together
+
     @wraps(f)
     async def wrapped(*args, **kwargs):
         start = time.time()
@@ -103,7 +103,7 @@ async def wrapped(*args, **kwargs):
 
 def time_function(f):
     """Time a sync function."""
-    # comment to keep black/flake8 happy together
+
     @wraps(f)
     def wrapped(*args, **kwargs):
         start = time.time()