repo: Remove a Python 2 related comment

The EnvironmentError exception was changed to OSError in commit
ae824fb2fc2770c84cc34c1956e4c76c8c972860.

Change-Id: I1b4ff742af409ec848131e82900e885c9f089f0c
Reviewed-on: https://gerrit-review.googlesource.com/c/git-repo/+/397757
Reviewed-by: Mike Frysinger <vapier@google.com>
Tested-by: Peter Kjellerstedt <peter.kjellerstedt@axis.com>
Commit-Queue: Peter Kjellerstedt <peter.kjellerstedt@axis.com>
diff --git a/repo b/repo
index 2dd9dd9..91bcc5b 100755
--- a/repo
+++ b/repo
@@ -1245,7 +1245,6 @@
             with open(path, "rb") as f:
                 data = f.read()
         except OSError:
-            # NB: EnvironmentError is used for Python 2 & 3 compatibility.
             # If we couldn't open the file, assume it's an old source tree.
             return None