sql: remove unnecessary AUTOINCREMENT ID generation

Currently, if we perform something like
CREATE TABLE t1 (
        s1 INTEGER PRIMARY KEY AUTOINCREMENT,
        s2 INTEGER,
        CHECK (s1 <> 19)
);
INSERT INTO t1 VALUES (18, NULL);
INSERT INTO t1 (s2) VALUES (NULL);

we generate a new identifier in VDBE, but in any other case we
generate it in BOX. That was needed since the CHECK did not work
properly. This is not necessary now, because CHECK was moved to
BOX due to issue tarantool#3691. After this patch all new identifiers will
be generated in BOX.

Part of tarantool#4188

src/box/sql/insert.c

@@ -628,10 +628,7 @@ sqlInsert(Parse * pParse,	/* Parser context */
 			if (j < 0 || nColumn == 0
 			    || (pColumn && j >= pColumn->nId)) {
 				if (i == (int) autoinc_fieldno) {
-					sqlVdbeAddOp2(v,
-							  OP_NextAutoincValue,
-							  space->def->id,
-							  iRegStore);
+					sqlVdbeAddOp2(v, OP_Null, 0, iRegStore);
 					continue;
 				}
 				struct Expr *dflt = NULL;

src/box/sql/vdbe.c

@@ -1168,33 +1168,6 @@ case OP_String: {          /* out2 */
 	break;
 }
 
-/* Opcode: NextAutoincValue P1 P2 * * *
- * Synopsis: r[P2] = next value from space sequence, which pageno is r[P1]
- *
- * Get next value from space sequence, which pageno is written into register
- * P1, write this value into register P2. If space doesn't exists (invalid
- * space_id or something else), raise an error. If space with
- * specified space_id doesn't have attached sequence, also raise an error.
- */
-case OP_NextAutoincValue: {
-	assert(pOp->p1 > 0);
-	assert(pOp->p2 > 0);
-
-	struct space *space = space_by_id(pOp->p1);
-	if (space == NULL)
-		goto abort_due_to_error;
-
-	int64_t value;
-	struct sequence *sequence = space->sequence;
-	if (sequence == NULL || sequence_next(sequence, &value) != 0)
-		goto abort_due_to_error;
-
-	pOut = out2Prerelease(p, pOp);
-	mem_set_i64(pOut, value);
-
-	break;
-}
-
 /* Opcode: Null P1 P2 P3 * *
  * Synopsis: r[P2..P3]=NULL
  *