Resetting style property via elt.style.xxx doesn't work

[paulrouget]

Here is an example. The div should turn transparent. It doesn't.

<div style="width:200px;height:200px;border:2px solid red;background:blue"></div>

<script>

  setTimeout(() => {
    document.querySelector("div").style.background = "";
  }, 1000);

</script>

[paulrouget]

This breaks React and virtual-dom based libraries.

[paulrouget]

Calling document.content_changed(node, NodeDamage::NodeStyleDamaged) in cssstyledeclaration.rs#RemoveProperty appears to fix this issue. I'll submit a PR.