fix corner case in side_effects (#5383)

fixes #5382

lib/compress.js

@@ -5426,7 +5426,6 @@ Compressor.prototype.compress = function(node) {
                 return !(prop instanceof AST_ObjectGetter || prop instanceof AST_Spread);
             });
         });
-        def(AST_ObjectIdentity, return_true);
         def(AST_Sequence, function() {
             return this.tail_node().safe_to_spread();
         });