Remove getdir from mjpResourceProvider.

All known implementations were effectively the same as the default fallback. It was just adding unneeded complexity. Removing this now will help with upcoming improvements to resource providers.

PiperOrigin-RevId: 855163273
Change-Id: I529fc18d0d03a8dc676c909ec9e4b1da1454d414

include/mujoco/mjplugin.h

@@ -42,10 +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 returning the directory of a resource
-// sets dir to directory string with ndir being size of directory string
-typedef void (*mjfGetResourceDir)(mjResource* resource, const char** dir, int* ndir);
-
 // 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
@@ -59,7 +55,6 @@ struct mjpResourceProvider {
   mjfOpenResource open;             // opening callback
   mjfReadResource read;             // reading callback
   mjfCloseResource close;           // closing callback
-  mjfGetResourceDir getdir;         // get directory callback (optional)
   mjfResourceModified modified;     // resource modified callback (optional)
   void* data;                       // opaque data pointer (resource invariant)
 };