Remove ClearSelection() from DragCaret::NodeWillBeRemoved()

This line was introduced before 2011 splitting DragCaretController from
 FrameSelection:
https://chromium.googlesource.com/chromium/src/+/fa14cd2b25316fb358f7f5ebc16f752ebcb4093a

Now DragCaret doesn't touch Selection Layout and this is unnecessary call.

BUG=708453

Review-Url: https://codereview.chromium.org/2813883005
Cr-Commit-Position: refs/heads/master@{#464356}
1 file changed