test_machines: remove no-longer relevant comment

The flake8 config excludes E741, which would complain about using
'l' (lower-case ell) as a variable name. We use this for the Lister object in
one test that uses single-character variable names for all the machines ('b'
for Boss, 'm' for Mailbox, etc). That comment was added before excluding
E741. If we ever restore that warning, we might want to rename the variable.

src/wormhole/test/test_machines.py

@@ -398,7 +398,6 @@ class Input(unittest.TestCase):
         events = []
         i = _input.Input(timing.DebugTiming())
         c = Dummy("c", events, ICode, "got_nameplate", "finished_input")
-        # renamed from l as l is indistinguishable from 1 in some fonts.
         l = Dummy("l", events, ILister, "refresh")
         i.wire(c, l)
         return i, c, l, events