fixed drop foreign key to be backwards compatible

go/libraries/doltcore/doltdb/foreign_key_coll.go

@@ -409,13 +409,18 @@ func (fkc *ForeignKeyCollection) Map(ctx context.Context, vrw types.ValueReadWri
 
 // RemoveKey removes a foreign key from the collection. It does not remove the associated indexes from their
 // respective tables.
-func (fkc *ForeignKeyCollection) RemoveKey(foreignKeyName string) (ForeignKey, error) {
-	fk, ok := fkc.GetByNameCaseInsensitive(foreignKeyName)
-	if !ok {
-		return fk, fmt.Errorf("`%s` does not exist as a foreign key", foreignKeyName)
+func (fkc *ForeignKeyCollection) RemoveKey(foreignKeyName string) error {
+	var key string
+	for k, fk := range fkc.foreignKeys {
+		if strings.ToLower(fk.Name) == strings.ToLower(foreignKeyName) {
+			key = k
+		}
 	}
-	delete(fkc.foreignKeys, fk.HashOf().String())
-	return fk, nil
+	if key == "" {
+		return fmt.Errorf("`%s` does not exist as a foreign key", foreignKeyName)
+	}
+	delete(fkc.foreignKeys, key)
+	return nil
 }
 
 // RemoveTables removes all foreign keys associated with the given tables, if permitted. The operation assumes that ALL

go/libraries/doltcore/doltdb/root_val.go

@@ -1224,7 +1224,7 @@ func (root *RootValue) ValidateForeignKeys(ctx context.Context) (*RootValue, err
 				return nil, err
 			}
 		} else {
-			_, err := fkCollection.RemoveKey(foreignKey.Name)
+			err := fkCollection.RemoveKey(foreignKey.Name)
 			if err != nil {
 				return nil, err
 			}

go/libraries/doltcore/sqle/tables.go

@@ -681,7 +681,7 @@ func (t *AlterableDoltTable) DropForeignKey(ctx *sql.Context, fkName string) err
 	if err != nil {
 		return err
 	}
-	_, err = fkc.RemoveKey(fkName)
+	err = fkc.RemoveKey(fkName)
 	if err != nil {
 		return err
 	}