Roll back VFS refactor due internal breakages

PiperOrigin-RevId: 856273160
Change-Id: I4097e05ed4e48ebee05b4347d0f227d4f39c1b09

include/mujoco/mjplugin.h

@@ -27,7 +27,6 @@
 struct mjResource_ {
   char* name;                                   // name of resource (filename, etc)
   void* data;                                   // opaque data pointer
-  mjVFS* vfs;                                   // pointer to the VFS
   char timestamp[512];                          // timestamp of the resource
   const struct mjpResourceProvider* provider;   // pointer to the provider
 };
@@ -43,12 +42,6 @@ typedef int (*mjfReadResource)(mjResource* resource, const void** buffer);
 // callback for closing a resource (responsible for freeing any allocated memory)
 typedef void (*mjfCloseResource)(mjResource* resource);
 
-// callback for mounting a resource (provider), returns zero on failure
-typedef int (*mjfMountResource)(mjResource* resource);
-
-// callback for unmounting a resource (provider), returns zero on failure
-typedef int (*mjfUnmountResource)(mjResource* resource);
-
 // callback for checking if the current resource was modified from the time
 // specified by the timestamp
 // returns 0 if the resource's timestamp matches the provided timestamp
@@ -62,8 +55,6 @@ struct mjpResourceProvider {
   mjfOpenResource open;             // opening callback
   mjfReadResource read;             // reading callback
   mjfCloseResource close;           // closing callback
-  mjfMountResource mount;           // mounting callback (optional)
-  mjfUnmountResource unmount;       // unmounting callback (optional)
   mjfResourceModified modified;     // resource modified callback (optional)
   void* data;                       // opaque data pointer (resource invariant)
 };