DiscIO: Remove VolumeCreator

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.

Source/Core/DiscIO/Volume.h

@@ -7,6 +7,7 @@
 #include <cstring>
 #include <limits>
 #include <map>
+#include <memory>
 #include <string>
 #include <vector>
 
@@ -112,4 +113,9 @@ protected:
   static const size_t NAMES_TOTAL_BYTES = NAME_BYTES_LENGTH * NUMBER_OF_LANGUAGES;
 };
 
+std::unique_ptr<IVolume> CreateVolumeFromFilename(const std::string& filename);
+std::unique_ptr<IVolume> CreateVolumeFromDirectory(const std::string& directory, bool is_wii,
+                                                   const std::string& apploader = "",
+                                                   const std::string& dol = "");
+
 }  // namespace