Remove detached headers

ListView was leaving header and footer views
in the detached state, which is a problem because
no view should be left in that state after a layout
calculation. This was also causing the view to never
received detached-from-window callback if
the ListView is detached while the header is not
visible.

This CL fixes an issue by traversing fixed views
and removing the ones that match the criteria.
To keep the behavior as similar as possible,
we still do not call startTmpDispatch on
fixed views unless we'll remove them.

Bug: 24490656
Change-Id: I8acfbd1a9d9b8b24c1c4b7692ef82cfe0f4d43a8