How to completely remove Garage Band from macOS?
On a fresh install of Sierra 10.12.2, the GarageBand files are:

/Applications/GarageBand

/Library/Application Support/GarageBand

/Library/Audio/Apple Loops/Apple/Apple Loops for GarageBand

/Library/Receipts/com.apple.pkg.GarageBand_AppStore.bom

/Library/Receipts/com.apple.pkg.GarageBand_AppStore.plist

/System/Library/Receipts/com.apple.pkg.MAContent10_AssetPack_0325_AppleLoopsGarageBand1.bom

/System/Library/Receipts/com.apple.pkg.MAContent10_AssetPack_0325_AppleLoopsGarageBand1.plist

~/Library/Application Scripts/com.apple.STMExtension.GarageBand

~/Library/Containers/com.apple.STMExtension.GarageBand


Delete those and you should be GarageBand free.

Notes:


You might want consider also removing /Library/Audio/Apple Loops/Apple and /Library/Application Support/Logic (those loops aren't GarageBand-specific — Logic Pro uses them, for example).
If you're comfortable with the command line, you can delete this list programmatically. I recommend using the tool trash. First copy the above list and save it in a new file. Then run

xargs trash &lt;pathtothefile


For example if you save the list on your Desktop as garageband-files-to-delete.txt, you'd run

xargs trash &lt;~/desktop/garageband-files-to-delete.txt


(this may require sudo. you could also use rm -rf instead of trash, but that's dangerous).