RFR 8242260: Remove customizable ContentSigner from jarsigner

[Weijun Wang]

I am thinking about removing the `jarsigner -altsigner -altsignerpath` options and underlying classes:

            JBS : https://bugs.openjdk.java.net/browse/JDK-8242260

Please review everything at:

   Release note : https://bugs.openjdk.java.net/browse/JDK-8242261
            CSR : https://bugs.openjdk.java.net/browse/JDK-8242262
         webrev : http://cr.openjdk.java.net/~weijun/8242260/webrev.00/

The CSR "Problem" section has more info on why it's better to remove it now.

Thanks,
Max