Just remove the packages for your distribution, for example in a debian base system just do:
root@windu:~# dpkg -l |grep vz
ii kernel-patch-openvz 028.18.1+etch6 server virtualization solution - kernel patc
ii linux-image-2.6.18+openvz custom01 Linux kernel binary image for version 2.6.18
ii vzctl 3.0.11-13 server virtualization solution - control too
ii vzquota 3.0.8-2 server virtualization solution - quota tools
root@windu:~#
Then just remove the openvz packages. Use the package manager of your own distribution (rpm, emerge, yum, apt ...)