refactor: Dedup tables only at the top level in FlattenTables (#1107)

Noticed this while working on #1106.
Don't think we need to dedup at each level of the recursion. Also not sure why we're deduping as table names should be unique

---

Author: erezrokah

schema/table.go

@@ -254,15 +254,21 @@ func (tt Tables) FilterDfs(tables, skipTables []string, skipDependentTables bool
 	return tt.FilterDfsFunc(include, exclude, skipDependentTables), nil
 }
 
-func (tt Tables) FlattenTables() Tables {
+func (tt Tables) flattenTablesRecursive() Tables {
 	tables := make(Tables, 0, len(tt))
 	for _, t := range tt {
 		table := *t
 		table.Relations = nil
 		tables = append(tables, &table)
-		tables = append(tables, t.Relations.FlattenTables()...)
+		tables = append(tables, t.Relations.flattenTablesRecursive()...)
 	}
 
+	return tables
+}
+
+func (tt Tables) FlattenTables() Tables {
+	tables := tt.flattenTablesRecursive()
+
 	seen := make(map[string]struct{})
 	deduped := make(Tables, 0, len(tables))
 	for _, t := range tables {