[minor] remove unused code

Author: qwazer

src/main/java/com/googlecode/scheme2ddl/exception/CannotGetDDLException.java

@@ -6,10 +6,6 @@
  */
 public class CannotGetDDLException extends Exception {
 
-    public CannotGetDDLException() {
-        super();
-    }
-
     public CannotGetDDLException(Throwable cause) {
         super(cause);
     }

src/main/java/com/googlecode/scheme2ddl/exception/NonSkippableException.java

@@ -5,8 +5,6 @@
  * @since Date: 03.07.2013
  */
 public class NonSkippableException extends Exception {
-    public NonSkippableException() {
-    }
 
     public NonSkippableException(Throwable cause) {
         super(cause);