Note that as of this release Adobe has a new common install location for plug-ins for this and future versions of CC. That location is:
Computer/Macintosh HD/Library/Application Support/Adobe/Plug-ins/CC/
You should drag your plug-ins to the above directory when installing.
If you have copied the plug-ins to the old location and now have two copies of the plug-ins appearing, you can just delete the plug-ins from the old location which is:
Computer/Macintosh HD/Applications/Adobe Photoshop CC 20NN/Plug-ins/
where "20NN" is your version of CC. For example "2015.5" or "2017".