/System/Library/CoreServices/Finder.app/Contents/Applications/AirDrop.app/Contents/MacOS/AirDrop
The binary is a part of AirDrop application.
/System/Library/PrivateFrameworks/FinderKit.framework/Versions/A/PlugIns/AirDrop.appex/Contents/MacOS/AirDrop
The binary is a part of FinderKit private framework.