Fix the issue that on tablet/unfold, the allapps background color is wrong.

As the new spec, it should use materialColorSurfaceDim for all devices.

Bug: 288493929
Test: manual, before: https://screenshot.googleplex.com/7YxpFGekwm6Gz6N, after: https://screenshot.googleplex.com/44Gr2dBfWSct7FK
Flag: no flag needed.
(cherry picked from https://googleplex-android-review.googlesource.com/q/commit:aa6612d3731a3e98f716747b0ede473e3bbca161)
Merged-In: Ic33d9a758fe9fbaa0f735c874a545df711a18e2f
Change-Id: Ic33d9a758fe9fbaa0f735c874a545df711a18e2f