How to 'unregister' a file type / MIME with launch services
Registering and unregistering apps and document types is done with: 

/System/Library/Frameworks/CoreServices.framework/Versions/A/Frameworks/LaunchServices.framework/Versions/A/Support/lsregister


To get help with the command simply use the h option.:

/System/Library/Frameworks/CoreServices.framework/Versions/A/Frameworks/LaunchServices.framework/Versions/A/Support/lsregister -h


In your case I would try to use the unregister option:

/System/Library/Frameworks/CoreServices.framework/Versions/A/Frameworks/LaunchServices.framework/Versions/A/Support/lsregister -u &lt;path to bundle&gt;


Depending on your app/bundle you may have to prepend a sudo and/or reboot afterwards.



Another step is to completely rebuild the launch services database:

/System/Library/Frameworks/CoreServices.framework/Versions/A/Frameworks/LaunchServices.framework/Versions/A/Support/lsregister -kill -r -domain local -domain system -domain user


and/or installing RCDefault.app and trying to remove the MIME/bundle/whatever - which is possible sometimes.