To remove Saffire MixControl you should locate and move the following files to the trash if they are available:
Macintosh HD/Applications/Saffire MixControl.app
Macintosh HD/System/Library/Extensions/Saffire.kext
Macintosh HD/Library/Startup Items/Saffire/.*
Macintosh HD/Library/Application Support/Saffire/.*
Macintosh HD/Library/Audio/MIDI Drivers/SaffireMIDIDriver.plugin
Macintosh HD/Users/[yourusername]/Library/Application Support/Focusrite/.*
Macintosh HD/Library/Receipts/Install Saffire MixControl.pkg
A * indicates that you should remove the entire folder