However, after downloading and installing the release version of Xcode 9.2 and trying to test using the Simulator I encountered the error:
unable to boot device because it cannot be located on disk
This error also included a link to a location within simulator files which obviously is no longer there due to the clean up process I had used. I tried a few options but eventually found a series of commands that clean this up and fixed the problem for me. Make sure to quite Xcode and the Simulator app first and then run these commands in Terminal:
sudo killall -9 com.apple.CoreSimulator.CoreSimulatorService
rm -rf ~/Library/Developer/CoreSimulator
rm -rf ~/Library/Developer/XCPGDevices
Hopefully after running them and starting Xcode the Simulator devices should all be functional again. Please note that if you have done any custom devices within your Simulator device list then these will have been deleted and the list reset to the default list of devices.