Revert "Allow only one return"

This reverts commit 18602d00a1.

boot/lexer.ll

@@ -125,6 +125,9 @@ return                  {
 cast                    {
                             return yy::parser::make_CAST(this->location);
                         }
+defer                   {
+                            return yy::parser::make_DEFER(this->location);
+                        }
 [A-Za-z_][A-Za-z0-9_]*  {
                             return yy::parser::make_IDENTIFIER(yytext, this->location);
                         }