Revert "Skip test until concurrent multi-user IME is enabled"

This reverts commit 7480497b.

Reason for revert: This should be fixed by now.

Bug: 345557347
Test: tested on sdk_car_md_x86_64_emulator
Test: atest ConcurrentMultiUserTest
Change-Id: I7908546b2f5efc7f49a066fc673ceb5106179924