Replace upvalue-based shell dispatch with OP_LUSH opcode

Add a dedicated OP_LUSH A B instruction that loads shell C functions
directly from the registry, eliminating the need for upvalue allocation
in mainfunc(), upvalue population in lua_load(), and the fragile
LUSH_NUM_UPVALS heuristic. Every chunk no longer carries 4 extra
upvalues.

lapi.c

@@ -29,7 +29,6 @@
 #include "ltm.h"
 #include "lundump.h"
 #include "lvm.h"
-#include "lcmd.h"
 
 
 
@@ -1136,27 +1135,6 @@ LUA_API int lua_load (lua_State *L, lua_Reader reader, void *data,
       setobj(L, f->upvals[0]->v.p, &gt);
       luaC_barrier(L, f->upvals[0], &gt);
     }
-    if (f->nupvalues >= LUSH_NUM_UPVALS) {  /* has lush upvalues? */
-      /* populate shell function upvalues from registry */
-      Table *regt = hvalue(&G(L)->l_registry);
-      TValue lushtv;
-      lu_byte tag = luaH_getint(regt, LUA_RIDX_LUSH, &lushtv);
-      if (novariant(tag) == LUA_TTABLE) {
-        static const char *const fields[] = {
-          "command", "interactive", "getenv", "setenv"
-        };
-        Table *lusht = hvalue(&lushtv);
-        int i;
-        for (i = 0; i < 4; i++) {
-          TValue val;
-          TString *key = luaS_new(L, fields[i]);
-          if (luaH_getstr(lusht, key, &val) != LUA_TNIL) {
-            setobj(L, f->upvals[i + 1]->v.p, &val);
-            luaC_barrier(L, f->upvals[i + 1], &val);
-          }
-        }
-      }
-    }
   }
   lua_unlock(L);
   return APIstatus(status);