code: public Signature dropLast(int n) {
          return new Signature(
                  methodType.dropParameterTypes(methodType.parameterCount() - n, methodType.parameterCount()),
                  Arrays.copyOfRange(argNames, 0, argNames.length - n));
      }
docs: Drop the specified number of last arguments from this signature.
  
  @param n number of arguments to drop
  @return a new signature