Revert "Treat process group creation failure due to a dead process as non-fatal"

This reverts commit 26cc4077.

Reason for revert: This change is not needed in the presence of aosp/2521297, which was the right fix for the problem. This change only introduces another problem (see b/297649601).

Bug: 297649601
Change-Id: If1656c7393790327396a80431c9bb7cc4738988a
Signed-off-by: Suren Baghdasaryan <surenb@google.com>