Revert "exec: fix up /proc/pid/comm in the execveat(AT_EMPTY_PATH) case"

This reverts commit b45605fa which is
commit 543841d1 upstream.

It breaks the Android kernel abi and can be brought back in the future
in an abi-safe way if it is really needed.

Bug: 161946584
Change-Id: I22e4874caa735da68f10a3d6477069f24bc0462d
Signed-off-by: Greg Kroah-Hartman <gregkh@google.com>