*: very minor changes to comments, function locations, and code

1. changed one comment;
2. changed one function locaiton in file to be more consistent;
3. added a code change that is consistent with the error message
but won't affect correctness.

Release justification:

pkg/sql/schemachanger/rel/schema_rules.go

@@ -80,16 +80,16 @@ func (sc *Schema) DefNotJoin1(name string, a Var, def func(a Var) Clauses) Rule1
 	return sc.rule(name, notJoin, def, a).(Rule1)
 }
 
-// DefNotJoin2 defines a not-join rule with two bound variable arguments.
-func (sc *Schema) DefNotJoin2(name string, a, b Var, def func(a, b Var) Clauses) Rule2 {
-	return sc.rule(name, notJoin, def, a, b).(Rule2)
-}
-
 // Def2 defines a Rule2.
 func (sc *Schema) Def2(name string, a, b Var, def func(a, b Var) Clauses) Rule2 {
 	return sc.rule(name, regular, def, a, b).(Rule2)
 }
 
+// DefNotJoin2 defines a not-join rule with two bound variable arguments.
+func (sc *Schema) DefNotJoin2(name string, a, b Var, def func(a, b Var) Clauses) Rule2 {
+	return sc.rule(name, notJoin, def, a, b).(Rule2)
+}
+
 // Def3 defines a Rule3.
 func (sc *Schema) Def3(name string, a, b, c Var, def func(a, b, c Var) Clauses) Rule3 {
 	return sc.rule(name, regular, def, a, b, c).(Rule3)

pkg/sql/schemachanger/scplan/internal/opgen/register.go

@@ -230,10 +230,10 @@ func validateTargets(targets []target) error {
 	}
 
 	for s := range allStatuses {
-		if !absentStatuses[s] {
+		if nonAbsentStatuses[s] && !absentStatuses[s] {
 			return errors.Errorf("status %s is featured in non-ABSENT targets but not in the ABSENT target", s)
 		}
-		if !nonAbsentStatuses[s] {
+		if absentStatuses[s] && !nonAbsentStatuses[s] {
 			return errors.Errorf("status %s is featured in ABSENT target but not in any non-ABSENT targets", s)
 		}
 	}

pkg/sql/schemachanger/scplan/internal/scgraph/graph.go

@@ -23,7 +23,7 @@ import (
 	"github.com/cockroachdb/redact"
 )
 
-// Graph is a graph whose nodes are *scpb.Nodes. Graphs are constructed during
+// Graph is a graph whose nodes are *screl.Nodes. Graphs are constructed during
 // schema change planning. Edges in the graph represent dependencies between
 // nodes, either due to the sequencing of statuses for a single target or due to
 // inter-target dependencies between statuses.