buildman: Drop a Python 2.7 comment

This is well out of date, but it is still reasonable to use a list. Drop
the comment.

Signed-off-by: Simon Glass <sjg@chromium.org>
diff --git a/tools/buildman/boards.py b/tools/buildman/boards.py
index b30b344..8a0971a 100644
--- a/tools/buildman/boards.py
+++ b/tools/buildman/boards.py
@@ -371,7 +371,6 @@
 class Boards:
     """Manage a list of boards."""
     def __init__(self):
-        # Use a simple list here, sinc OrderedDict requires Python 2.7
         self._boards = []
 
     def add_board(self, brd):