Files in System32 are typically owned by "TrustedInstaller" and are locked down very tightly. There is no direct way to remove / delete files under this folder.
This is done to ensure that there is no misbehavior done by any malware or user and that the system remains stable.
If you really, absolutely feel you must do this, the easiest way is to boot from a Linux LiveCD or a Windows install disk.
Using Linux, mount the drive R/W with the ntfs-3g utility (or just use mount; all modern Linux distros default to using ntfs-3g) and delete the files like you would any others (from a shell, the command is rm). I know this approach works.
Using Windows install media, you need to enter repair / recovery mode. That will give you the option to open a command prompt. This prompt can be used to browse to the folder (note that it may not be on the C: drive, if the install media is putting itself as C:) and try deleting the file, potentially using the same kinds of things you did above (taking ownership, changing ACLs, etc.). This should work, but I haven't tested it.
You could try to start CMD in administrator mode and then delete the files with the DEL command provided if some other process is not locking the file.
Being Administrator, you can directly rename the files only they are not being used by any of the processes but deletions of sys files in the drivers folder is not allowed directly.
I am awaiting a reply from the support team regarding my license activation issue. Once I get a reply, I will make one more attempt to do a clean install by renaming / deleting the leftover files and see if it works.
Thank you all for your help. I'll keep you posted once I'm done so that it helps others.