Fix faulty compression

`String(x + 5)` is not always the same as `x + "5"`.  Overlooked that. :-(

Close #350

lib/compress.js

@@ -2031,16 +2031,6 @@ merge(Compressor.prototype, {
             && self.right.getValue() === "" && self.left instanceof AST_Binary
             && self.left.operator == "+" && self.left.is_string(compressor)) {
             return self.left;
-        } else if (self.operator == "+" && self.right instanceof AST_String
-                   && self.right.getValue() === "" && self.left instanceof AST_Binary
-                   && self.left.operator == "+" && self.left.right instanceof AST_Number) {
-            return make_node(AST_Binary, self, {
-                left: self.left.left,
-                operator: "+",
-                right: make_node(AST_String, self.right, {
-                    value: String(self.left.right.value)
-                })
-            });
         }
         if (compressor.option("evaluate")) {
             if (self.operator == "+") {

test/compress/issue-269.js

@@ -54,15 +54,13 @@ strings_concat: {
 	input: {
 		f(
 			String(x + 'str'),
-			String('str' + x),
-			String(x + 5)
+			String('str' + x)
 		);
 	}
 	expect: {
 		f(
 			x + 'str',
-			'str' + x,
-			x + '5'
+			'str' + x
 		);
 	}
 }