Fix deallocate not properly cleaning `objects` arrray in Javascript

[LiveDuo]

From: https://www.reddit.com/r/rust/comments/1i0hcrt/comment/m706d2x/

Just to clarify: I'm just talking about the length of the objects array in JavaScript, which currently appears only to ever grow as changes happen on the page. (For example if you set a timer to switch the tasks list from 1 task to 0 tasks every few milliseconds, and then keep checking objects.length you'll see it just gets longer and longer, even though most of the entries in it are undefined)

Relevant code: https://github.com/LiveDuo/tinyweb/blob/master/src/js/main.js#L94