rangelib.py: Remove the obsolete comment line.

It was supposed to be removed in [1], but still exists for unknown
reason.

[1]: commit e8f756137c

Change-Id: Ic51e14085294495ec390bbf3cbe8c4fb6e97b860

tools/releasetools/rangelib.py

@@ -24,7 +24,6 @@ class RangeSet(object):
   lots of runs."""
 
   def __init__(self, data=None):
-    # TODO(tbao): monotonic is broken when passing in a tuple.
     self.monotonic = False
     if isinstance(data, str):
       self._parse_internal(data)