Remove node key from document marker set in Node::didMoveToNewDocument

This patch makes |Node::didMoveToNewDocument| to remove marked node from old document's marker set.

Removal of node key from marker set is similar to node key removal from AXObjectCache. Both removal should be happened in same places.

This patch fixes regression introduced by
https://codereview.chromium.org/98273002, which changed marker set update from |Document::nodeWillBeRemoved| to |Node::willBeDeletedFromDocument|.

BUG=360214
TEST=DocumentMarkerControllerTest.DidMoveToNewDocument

Review URL: https://codereview.chromium.org/236803002

git-svn-id: svn://svn.chromium.org/blink/trunk@171527 bbb929c8-8fbe-4397-9dbb-9b2b20218538