Remove unused methods from java.util.zip.ZipFile

The following java.util.zip.ZipFile methods:
hashN(byte[],int,int)
hash_append(int,byte)

were removed here:
https://github.com/openjdk/jdk/commit/d2e0d0e06a9fb93c4edb8d9f67aa068775e1c199#diff-dd9ce07ffe773a559eb2182c5fa3d0b11b90b53e109934084f53e1ed7988bf57L71

and then reintroduced possibly in a merge mistake here: https://github.com/openjdk/jdk/commit/1982432db4e35626cfe693e0ec6bbc72fa32a24e

Those private methods are unused, hence can be safely removed.