vfs: Remove InterpretAsDirectory and related functions

When writing VFS, it initally seemed useful to include a function to in-place convert container files into directories in one homogenous directory structure, but re-evaluating it now there have been plenty of chances to use it and there has always been a better way. Removing as it is unused and likely will not be used.

src/core/file_sys/vfs_real.h

@@ -100,9 +100,6 @@ public:
     std::string GetFullPath() const override;
     std::map<std::string, VfsEntryType, std::less<>> GetEntries() const override;
 
-protected:
-    bool ReplaceFileWithSubdirectory(VirtualFile file, VirtualDir dir) override;
-
 private:
     RealVfsDirectory(RealVfsFilesystem& base, const std::string& path, Mode perms = Mode::Read);