Fix z-index of local overlay

Local overlay z-index is positioning overlay items (phantoms, etc)
above the floated toolbar. The overlay container is a sibling to the
toolbar's parent and is later in the DOM. z-indexing is
unnecessary and has been removed.

Bug: 50096
Change-Id: Ib46f66b1d1bea36d761f793e9966e09db6e675ca
Merge "Fix z-index of local overlay"