Ubuntu Got 2 Windows 7 (loader) entries in Grub2

What was the cause of the problem:

Grub2 looks for the Windows boot files for detecting Windows entries. Though you removed Windows 7, the Windows 7 boot files aren't removed (which are "Boot" folder and "bootmgr" file). And as Windows 7 boot files are there, grub2 simply assumes that, there are Windows 7 installation also. Hence the dual entry.

You should find what you're looking for inside of /boot/grub/grub.cfg. This file is dynamically generated by update-grub2. I am dual booting Ubuntu 32bit and 64bit. If I wanted to remove one, I would simply delete it's section from this file.

menuentry 'Ubuntu, with Linux 3.2.0-23-generic' --class ubuntu --class gnu-linux --class gnu --class os {
 ### BEGIN /etc/grub.d/30_os-prober ###

menuentry "Windows 7 (loader) (on /dev/sda1)" --class windows --class os {
    insmod part_msdos
    insmod ntfs
    set root='(hd0,msdos2)'
    search --no-floppy --fs-uuid --set=root C08C7F598C7F4944
    chainloader +1
}
menuentry "Windows 7 (loader) (on /dev/sda2)" --class windows --class os {
    insmod part_msdos
    insmod ntfs
    set root='(hd0,msdos2)'
    search --no-floppy --fs-uuid --set=root C08C7F598C7F4944
    chainloader +1
}
menuentry "Windows Recovery Environment (loader) (on /dev/sda4)" --class windows --class os {
    insmod part_msdos
    insmod ntfs
    set root='(hd0,msdos4)'
    search --no-floppy --fs-uuid --set=root C22A7EEA2A7EDB3D
    drivemap -s (hd0) ${root}
    chainloader +1

Changes should take effect immediately, so make a backup and be careful. Also, anything you change in this file will be completely over written if you run update-grub2 again.

make sure you're delete the right one or you'll be sorry...

OR


Mount the /dev/sda1 drive. Then in that drive look for a folder named Boot and a file named bootmgr. Remove both the folder and file. Then run update-grub2 command again.
You might want to install grub2 again. As I see your Ubuntu installation is at /dev/sdb, the commands will be

sudo grub-install /dev/sdb
sudo update-grub 

Bye..