DiscIO/VolumeWii: Decouple "is encrypted" from "is hashed"

Needed for the next commit. NFS disc images are hashed but not encrypted.

While we're at it, also get rid of SupportsIntegrityCheck.
It does the same thing as old IsEncryptedAndHashed and new HasWiiHashes.

Source/Core/DiscIO/DiscExtractor.cpp

@@ -286,7 +286,7 @@ bool ExportSystemData(const Volume& volume, const Partition& partition,
     success &= ExportTicket(volume, partition, export_folder + "/ticket.bin");
     success &= ExportTMD(volume, partition, export_folder + "/tmd.bin");
     success &= ExportCertificateChain(volume, partition, export_folder + "/cert.bin");
-    if (volume.IsEncryptedAndHashed())
+    if (volume.HasWiiHashes())
       success &= ExportH3Hashes(volume, partition, export_folder + "/h3.bin");
   }