A duplicate iPhone simulator just appeared after I deleted ~/Library/Developer/Xcode/CoreSimulator
folder
I have a same issue after installing Xcode beta version. I found that there are several solution to fix this issue.
https://github.com/fastlane/fastlane/tree/master/snapshot
usage : gem install fastlane; fastlane snapshot reset_simulators
I solved my problem with this library and it is very simple to use.
You can check installed simulators and delete them. But it will take too long time if you have many simulators.
you can use xcrun command in terminal. But you need to input a specific device name with command.