Sparse ten_J and ten_J_colind memory

PiperOrigin-RevId: 868800229
Change-Id: I7130b0316a64aefc5b6eeba00482cfc2f5bedb21

Author: thowell

mjpc/simulate.cc

@@ -577,9 +577,6 @@ void UpdateWatch(mj::Simulate* sim) {
   sim->ui0.sect[SECT_WATCH].item[2].multi.nelem = 1;
   mju::strcpy_arr(sim->ui0.sect[SECT_WATCH].item[2].multi.name[0], "invalid field");
 
-  // prepare symbols needed by xmacro
-  MJDATA_POINTERS_PREAMBLE(sim->m);
-
   // find specified field in mjData arrays, update value
   #define X(TYPE, NAME, NR, NC)                                                                  \
     if (!mju::strcmp_arr(#NAME, sim->field) &&                                                   \