From someone who actually also was experiencing this problem who came here for help on this as well, I found that Indrek's solution was the only workable one for me.
Drive Genius does not place files in
~/Library/Contextual Menu Items which is where you would expect to find something like this.
Here is what worked for me to remove the Drive Genius 3 contextual menu item
- Delete the application
/Library/Application Support/Drive Genius
I had tried deleting preference files and other seemingly related files and rebooting and that did not have an impact on this problem.
Also note: To get rid of other useless files and effects left by this program after you shut it off in all its settings (which it may ignore) and it still leaves behind the system pull down menu extra icon that goes near the clock, I find that removing all three "prosoft" and "Drive Genius" items it tucks away into
/Library/LaunchDaemons such as the definitely secure-deletion-related
"com.prosofteng.DriveGenius.locum.plist" file and rebooting wipes that after-effect out as well.