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.cpp

@@ -430,7 +430,4 @@ std::map<std::string, VfsEntryType, std::less<>> RealVfsDirectory::GetEntries()
     return out;
 }
 
-bool RealVfsDirectory::ReplaceFileWithSubdirectory(VirtualFile file, VirtualDir dir) {
-    return false;
-}
 } // namespace FileSys