Do not embed activity on a hidden TaskFragment

Home activity was started again when the existing instance was
removed. Somehow, the new home activity was unexpected embedded
into a hidden TaskFragment on home task, which is going to be
removed soon.

Bug: 402126069
Test: verified via the steps on the bug
Flag: EXEMPT bugfix
Change-Id: I4367a75ecb2782d06df8a77b71878d7378a44252