show trust id activity button only if available

OpenKeychain/src/main/res/layout/key_list_item.xml

@@ -2,7 +2,6 @@
 <LinearLayout
     xmlns:android="http://schemas.android.com/apk/res/android"
     xmlns:tools="http://schemas.android.com/tools"
-
     android:layout_width="match_parent"
     android:layout_height="wrap_content"
     android:minHeight="?attr/listPreferredItemHeight"

OpenKeychain/src/main/res/layout/view_key_trust_id_item.xml

@@ -35,6 +35,8 @@
         android:id="@+id/trust_id_action"
         android:background="?selectableItemBackground"
         android:src="@drawable/ic_chat_black_24dp"
+        android:visibility="gone"
+        tools:visibility="visible"
         />
 
 </LinearLayout>