Yes. You can use gparted to delete the windows partition (remember to back-up files first), then resize the Linux partition to take up the entire drive.
Grub should automatically detect that windows has been removed. If it doesn't, you can edit the Grub config fairly easily to tell it to not show options on boot, just boot straight into Linux.
There is also an option to remember the last OS booted, and if no button is pressed for 10 seconds during boot, it will continue to that OS.