Add edge ids to flex elements in mjModel.

PiperOrigin-RevId: 675130981
Change-Id: If2ccfb268142d235273b7a50e15740f6399903b2

plugin/elasticity/solid.h

@@ -42,13 +42,8 @@ class Solid {
   int i0;  // index of first body
   int nc;  // number of cubes in the grid
   int nv;  // number of vertices (bodies) in the solid
-  int nt;  // number of volumetric elements (tetrahedra)
   int ne;  // number of edges in the solid
 
-  // connectivity info for mapping tetrahedra to edges and vertices
-  std::vector<Stencil3D> elements;          // 4 vertices and 6 edges (nt x 10)
-  std::vector<std::pair<int, int> > edges;  // edge to vertex map     (ne x 2)
-
   // precomputed quantities
   std::vector<mjtNum> prev;                 // previous-step lengths  (ne x 1)
   std::vector<mjtNum> elongation;           // edge elongation        (ne x 1)
@@ -58,8 +53,7 @@ class Solid {
 
  private:
   Solid(const mjModel* m, mjData* d, int instance, mjtNum nu, mjtNum E,
-        mjtNum damp, const std::vector<int>& simplex,
-        const std::vector<int>& edgeidx);
+        mjtNum damp);
 };
 
 }  // namespace mujoco::plugin::elasticity