RFR: JDK-8223723: j.l.c.MethodTypeDesc.dropParameterTypes​ throws the undocumented exception: IllegalArgumentException

[Vicente Romero]

Please review fix for [1] at [2]. The implementation of method 
java.lang.constant.MethodTypeDesc::dropParameterTypes was throwing a non 
specified exception. The proposed fix is synchronizing the 
implementation with the specification. Please also review the CSR at 
[3]. Check the problem section in the CSR for more details,

Thanks,
Vicente
[1] https://bugs.openjdk.java.net/browse/JDK-8223723
[2] http://cr.openjdk.java.net/~vromero/8223767/webrev.00/
[3] https://bugs.openjdk.java.net/browse/JDK-8223918