database/sql: fix Rows.Columns() documentation

Fixes #27202

Change-Id: I83620748a81500e433795c7b2b7f13399d17f777
GitHub-Last-Rev: 64457e12ceaa408efc7f75091f1b30c35b8e5d44
GitHub-Pull-Request: golang/go#27472
Reviewed-on: https://go-review.googlesource.com/133057Reviewed-by: Daniel Theophanes <kardianos@gmail.com>

src/database/sql/sql.go

@@ -2735,8 +2735,7 @@ func (rs *Rows) Err() error {
 }
 
 // Columns returns the column names.
-// Columns returns an error if the rows are closed, or if the rows
-// are from QueryRow and there was a deferred error.
+// Columns returns an error if the rows are closed.
 func (rs *Rows) Columns() ([]string, error) {
 	rs.closemu.RLock()
 	defer rs.closemu.RUnlock()