Locate the AU/VST/RTAS/AAX plug-ins folders (listed below) on your computer, and delete the plug-ins you don't want.

Audio Units (Components):

HD/Library/Audio/Plug-Ins/Components

VST:

HD/Library/Audio/Plug-Ins/VST

RTAS:

HD/Library/Application Support/Digidesign/Plug-Ins

AAX:

HD/Library/Application Support/Avid/Audio/Plug-Ins