Remove .tagName from ce.MWInlineImageNode

Was unused, because this.$ is always overwritten in the constructor

Change-Id: I4d403f1b89351fb7d23131f944406d5a088fdeef
Remove ve.ce.ImageNode.prototype.onUpdate

Was empty.

Bonus: consistently use object style for .attr(), was already
used for .css()

Change-Id: Idd0592d6f30388c9952e110ff6fff008bb465877
Remove ve.ce.Node.prototype.onAttributeChange

There was code in there once, but it's now empty. Removed it in favor
of adding explicit listeners in the handful of subclasses that
override it.

Change-Id: I160e55ad3c7d85c9f830a4bd7d42ec5dc18ad04f
Merge changes I160e55ad,Idd0592d6,I4d403f1b

* changes:
  Remove ve.ce.Node.prototype.onAttributeChange
  Remove ve.ce.ImageNode.prototype.onUpdate
  Remove .tagName from ce.MWInlineImageNode