Remove "global" option from [compiler/coordinate](https://mujoco.readthedocs.io/en/latest/XMLreference.html#compiler-coordinate) attribute.

Keeping this rarely-used setting complicates the compiler logic and is blocking future improvements. In order to convert older models which used this option, load and save them in MuJoCo 2.3.3 or older.

PiperOrigin-RevId: 521739137
Change-Id: If0cb40d5db4879a4db9318cc2be258a7923e6e85

src/user/user_model.h

@@ -123,7 +123,6 @@ class mjCModel {
   bool balanceinertia;            // automatically impose A + B >= C rule
   bool strippath;                 // automatically strip paths from mesh files
   bool fitaabb;                   // meshfit to aabb instead of inertia box
-  bool global;                    // local or global coordinates
   bool degree;                    // angles in radians or degrees
   char euler[3];                  // sequence for euler rotations
   std::string meshdir;            // mesh and hfield directory