Handle revoked and expired keys in decrypt activity

OpenKeychain/src/main/res/values-ja/strings.xml

@@ -254,7 +254,7 @@
   </plurals>
   <!--results shown after decryption/verification-->
   <string name="decrypt_result_invalid_signature">不正な署名です!</string>
-  <string name="decrypt_result_signature_unknown_pub_key">不明な公開鍵</string>
+  <string name="decrypt_result_signature_missing_key">不明な公開鍵</string>
   <string name="decrypt_result_signature_uncertified">正しい署名 (未証明)</string>
   <string name="decrypt_result_signature_certified">正しい署名 (証明ずみ)</string>
   <string name="decrypt_result_decrypted">復号化に成功した</string>