Fix Unusable signing key not properly disabled, Issue #1468

Signed-off-by: Durgesh <007durgesh219@gmail.com>

OpenKeychain/src/main/java/org/sufficientlysecure/keychain/ui/widget/CertifyKeySpinner.java

@@ -113,11 +113,6 @@ public class CertifyKeySpinner extends KeySpinner {
 
     @Override
     boolean isItemEnabled(Cursor cursor) {
-        // "none" entry is always enabled!
-        if (cursor.getPosition() == 0) {
-            return true;
-        }
-
         if (cursor.getInt(KeyAdapter.INDEX_IS_REVOKED) != 0) {
             return false;
         }

OpenKeychain/src/main/java/org/sufficientlysecure/keychain/ui/widget/SignKeySpinner.java

@@ -72,11 +72,6 @@ public class SignKeySpinner extends KeySpinner {
 
     @Override
     boolean isItemEnabled(Cursor cursor) {
-        // "none" entry is always enabled!
-        if (cursor.getPosition() == 0) {
-            return true;
-        }
-
         if (cursor.getInt(KeyAdapter.INDEX_IS_REVOKED) != 0) {
             return false;
         }