inlineStyles plugin should not remove id attribute from target element

[johnkenny54]

When the inlineStyles plugin inlines a style with an id selector, it is removing the id attribute from the target element. It shouldn't do this, as it has no way of knowing whether the id is used elsewhere.

To Reproduce
Optimize the following with the inlineStyles plugin:

<svg xmlns="http://www.w3.org/2000/svg" viewBox="0 0 20 20">
  <style>
    #a {stroke:red;}
  </style>
  <path id="a" d="M 2 2 h10"/>
  <use href="#a" x="5" y="5"/>
</svg>

Expected behavior
The style should be inlined, but the id attribute should not be deleted.

Version 4.0.0-rc.1