The files are called ‘com.blokas.Midihub Editor.plist’ and ‘com.blokas.midihub-editor.plist’. You may use the Finder to remove the files, there should be two possible locations:
/Users/joeperkins/Library/Preferences
/Library/Preferences
You can use ‘Go->Go to Folder’ menu item to enter the path directly.
Then make sure to run the killall command.