remove default and implementation from interface

android/src/main/java/im/status/keycard/android/NFCCardChannel.java

@@ -34,4 +34,8 @@ public class NFCCardChannel implements CardChannel {
   public boolean isConnected() {
     return this.isoDep.isConnected();
   }
+
+  public int pairingPasswordPBKDF2IterationCount() {
+    return 50000;
+  }
 }

desktop/src/main/java/im/status/keycard/desktop/PCSCCardChannel.java

@@ -47,4 +47,8 @@ public class PCSCCardChannel implements CardChannel {
   public boolean isConnected() {
     return true;
   }
+
+  public int pairingPasswordPBKDF2IterationCount() {
+    return 50000;
+  }
 }

lib/src/main/java/im/status/keycard/io/CardChannel.java

@@ -29,7 +29,5 @@ public interface CardChannel {
    *
    * @return the iteration count
    */
-  default int pairingPasswordPBKDF2IterationCount() {
-    return 50000;
-  }
+  int pairingPasswordPBKDF2IterationCount();
 }