If you'd like to remove Vista drive and only have Windows 7, you need to mark Windows 7 active in Disk Management, shutdown and unplug the Vista drive, then boot into Windows 7 DVD Repair console to run Startup Repair 3 separate times as it will attempt to repair and then rewrite the MBR to Windows 7.
If you'd like to confirm these standard recovery steps apply to your configuration, please post back a screenshot of your full Disk Management drive map, using Snipping Tool in Start Menu, attaching file using paper clip in replay box.
We have helped remove 100+ dual boots here since Windows 7 release with a nearly perfect success rate.