Revert "database/sql: prevent race in driver by locking dc in Next"

This reverts commit 897080d5cbb1793f8ad3ef5fb7c6fafba2e97d42.

Reason for revert: Fails to fix all the locking issues.

Updates #21117

Change-Id: I6fc9cb7897244d6e1af78c089a2bf383258ec049
Reviewed-on: https://go-review.googlesource.com/71450
Reviewed-by: Ian Lance Taylor <iant@golang.org>
diff --git a/src/database/sql/sql_test.go b/src/database/sql/sql_test.go
index 760159a..046d95a 100644
--- a/src/database/sql/sql_test.go
+++ b/src/database/sql/sql_test.go
@@ -3127,9 +3127,6 @@
 // In the test, a context is canceled while the query is in process so
 // the internal rollback will run concurrently with the explicitly called
 // Tx.Rollback.
-//
-// The addition of calling rows.Next also tests
-// Issue 21117.
 func TestIssue18429(t *testing.T) {
 	db := newTestDB(t, "people")
 	defer closeDB(t, db)
@@ -3140,7 +3137,7 @@
 
 	const milliWait = 30
 
-	for i := 0; i < 1000; i++ {
+	for i := 0; i < 100; i++ {
 		sem <- true
 		wg.Add(1)
 		go func() {
@@ -3162,9 +3159,6 @@
 			// reported.
 			rows, _ := tx.QueryContext(ctx, "WAIT|"+qwait+"|SELECT|people|name|")
 			if rows != nil {
-				// Call Next to test Issue 21117 and check for races.
-				for rows.Next() {
-				}
 				rows.Close()
 			}
 			// This call will race with the context cancel rollback to complete