Remove control plugin API.

This is a rollback of f937ffd93326b2964e33689b0dc6024124776a9e.

PiperOrigin-RevId: 507456400
Change-Id: I2026510e6065eb440c0c899fcc5a2cc8ff5afd49

src/engine/engine_forward.c

@@ -775,30 +775,9 @@ void mj_forwardSkip(const mjModel* m, mjData* d, int skipstage, int skipsensor)
   }
 
   // acceleration-dependent
-  if (!mjDISABLED(mjDSBL_ACTUATION)) {
-    // call legacy control callback if specified
-    if (mjcb_control) {
-      mjcb_control(m, d);
-    }
-
-    // handle control plugins
-    if (m->nplugin) {
-      const int nslot = mjp_pluginCount();
-      for (int i=0; i<m->nplugin; i++) {
-        const int slot = m->plugin[i];
-        const mjpPlugin* plugin = mjp_getPluginAtSlotUnsafe(slot, nslot);
-        if (!plugin) {
-          mju_error_i("invalid plugin slot: %d", slot);
-        }
-        if (plugin->capabilityflags & mjPLUGIN_CONTROL) {
-          if (!plugin->compute) {
-            mju_error_i("`compute` is a null function pointer for plugin at slot %d", slot);
-          }
-          plugin->compute(m, d, i, mjPLUGIN_CONTROL);
-        }
-      }
-    }
-}
+  if (mjcb_control && !mjDISABLED(mjDSBL_ACTUATION)) {
+    mjcb_control(m, d);
+  }
 
   mj_fwdActuation(m, d);
   mj_fwdAcceleration(m, d);