Revert "Run inflations of UMO in a background thread"

This reverts commit a88fd507.

Reason for revert: To fix b/271967119, this revert will not affect the status of b/269224904

Fixes: 271967119
Bug: 269224904
Test: atest MediaCarouselControllerTest

Change-Id: I229a60a8137e4881536b7271cbc5b2855b3f7d7a