MDEV-25496 Assertion 'trx->bulk_insert' failed on INSERT

row_get_prebuilt_insert_row(): Remove some fallback code that had been
added in commit 8ea923f5 (MDEV-24818).
It seems that after all, statement boundaries are being reliably
indicated by ha_innobase::start_stmt() or
(for partitioned tables) ha_innobase::external_lock().

mysql-test/suite/innodb/r/insert_into_empty.result

@@ -174,3 +174,11 @@ COMMIT;
 SET autocommit=1;
 DROP TABLE t1;
 DROP TEMPORARY TABLE t0;
+#
+# MDEV-25496 Assertion 'trx->bulk_insert' failed
+# in trx_undo_report_row_operation on INSERT
+#
+CREATE TABLE t (i INT) ENGINE=InnoDB PARTITION BY HASH (i) PARTITIONS 2;
+INSERT INTO t VALUES (0);
+INSERT INTO t VALUES (1),(0),(1);
+DROP TABLE t;

mysql-test/suite/innodb/t/insert_into_empty.test

 --source include/have_innodb.inc
 --source include/have_sequence.inc
 --source include/maybe_debug.inc
+--source include/have_partition.inc
 
 # Enable MDEV-515 table-level undo logging for insert into empty table
 SET foreign_key_checks=0, unique_checks=0;
@@ -183,3 +184,12 @@ COMMIT;
 SET autocommit=1;
 DROP TABLE t1;
 DROP TEMPORARY TABLE t0;
+
+--echo #
+--echo # MDEV-25496 Assertion 'trx->bulk_insert' failed
+--echo # in trx_undo_report_row_operation on INSERT
+--echo #
+CREATE TABLE t (i INT) ENGINE=InnoDB PARTITION BY HASH (i) PARTITIONS 2;
+INSERT INTO t VALUES (0);
+INSERT INTO t VALUES (1),(0),(1);
+DROP TABLE t;

storage/innobase/row/row0mysql.cc

@@ -1051,13 +1051,6 @@ row_get_prebuilt_insert_row(
 		if (prebuilt->trx_id == table->def_trx_id
 		    && prebuilt->ins_node->entry_list.size()
 		    == UT_LIST_GET_LEN(table->indexes)) {
-
-			if (prebuilt->trx->bulk_insert
-			    && prebuilt->ins_node->trx_id
-			       != prebuilt->trx->id) {
-				prebuilt->trx->bulk_insert = false;
-			}
-
 			return(prebuilt->ins_node->row);
 		}