This file is pretty small now that it doesn't handle Wii
partitions anymore, so let's move its contents to Volume.cpp.
This is also more consistent with how blob creation works.

Basically inlining GetDiscType into CreateVolumeFromFilename.

By removing mutable state in VolumeWiiCrypted, this change makes
partition-related code simpler. It also gets rid of other ugly things,
like ISOProperties's "over 9000" loop that creates a list of
partitions by trying possible combinations, and DiscScrubber's
volume swapping that recreates the entire volume when it needs to
change partition.

These disc images are encrypted and signed using a different set of keys.
We only care about the master key, so we check the signature issuer. If
it matches the debug issuer, then we'll use the RVT-R key. Otherwise,
the previous set of common and Korean keys are used.

These logs are very rarely useful and cause the issue
https://bugs.dolphin-emu.org/issues/9767

Rather than rely on the developer to do the right thing,
just make the default behavior safely deallocate resources.

If shared semantics are ever needed in the future, the
constructor that takes a unique_ptr for shared_ptr can
be used.