autofree: fix unused var error

vlib/v/gen/cgen.v

@@ -1037,12 +1037,12 @@ fn (mut g Gen) stmt(node ast.Stmt) {
 		}
 		ast.Return {
 			g.write_defer_stmts_when_needed()
-			af := g.pref.autofree && node.exprs.len > 0 && node.exprs[0] is ast.CallExpr && !g.is_builtin_mod
+			// af := g.pref.autofree && node.exprs.len > 0 && node.exprs[0] is ast.CallExpr && !g.is_builtin_mod
-			if g.pref.autofree {
+			af := g.pref.autofree && !g.is_builtin_mod
+			if af {
 				g.writeln('// ast.Return free')
 				// g.autofree_scope_vars(node.pos.pos - 1, node.pos.line_nr, true)
 				g.writeln('// ast.Return free_end')
-				// g.write_autofree_stmts_when_needed(node)
 			}
 			g.return_statement(node)
 		}

vlib/v/gen/fn.v

@@ -181,17 +181,6 @@ fn (mut g Gen) gen_fn_decl(it ast.FnDecl, skip bool) {
 	}
 }
 
-/*
-fn (mut g Gen) write_autofree_stmts_when_needed(r ast.Return) {
-	// TODO: write_autofree_stmts_when_needed should account for the current local scope vars.
-	// TODO: write_autofree_stmts_when_needed should not free the returned variables.
-	// It may require rewriting g.return_statement to assign the expressions
-	// to temporary variables, then protecting *them* from autofreeing ...
-	// g.writeln('// autofreeings before return:              -------')
-	// g.writeln(g.autofree_scope_vars(g.fn_decl.body_pos.pos))
-	// g.writeln('//--------------------------------------------------- ') // //g.write( g.autofree_scope_vars(r.pos.pos) )
-}
-*/
 fn (mut g Gen) write_defer_stmts_when_needed() {
 	if g.defer_stmts.len > 0 {
 		g.write_defer_stmts()