Since ActiveMatrix Decisions is installed on top of (that is, in the same TIBCO_HOME) as ActiveMatrix BPM, you can use the uninstaller provided in the aforementioned directory to also uninstall ActiveMatrix Decisions.
Note, however that uninstalling ActiveMatrix Decisions has no affect on Decisions Product IT applications that have been created in ActiveMatrix Administrator and deployed to a node. It only removes the
application template from the system so that it is no longer available from ActiveMatrix Administrator, preventing additional Decisions Product IT applications from being created and deployed. (The uninstall also removes files from the file system.)