Remove unused code in nova/api/ec2/__init__.py

"result = None" in nova/api/ec2/__init__.py#L546 is unused code, remove it

Change-Id: I1b09d8656686bafcc7f42bc77d01f3e14aa51ed9
Closes-Bug: #1265408
Merge "Remove unused code in nova/api/ec2/__init__.py"