Do not prebind sticky slices.

We have a precheck mechanism to filter out slices that are not eligible
to be displayed on the homepage. Since sticky cards are designed to
be always available, which implies they will never be null, so skip
prechecking on them.

This allows us to prevent from the precheck timeout which usually leads
to the disappearance of cards.

Fixes: 152365480
Test: robotests
Change-Id: Ic9e3df8b55609e9b5d1d3fd3a8d95e4086d3d7a4