Polish logic on initializing PGP keys.

- simplify interfaces
- more robust

pass/Helpers/Utils.swift

@@ -79,7 +79,6 @@ class Utils {
         Defaults.remove(.pgpPrivateKeyArmor)
         Defaults.remove(.pgpPrivateKeyURL)
         Defaults.remove(.pgpPublicKeyURL)
-        Defaults.remove(.pgpKeyID)
         Utils.removeKeychain(name: ".pgpKeyPassphrase")
     }