Revert "bpf, sockmap: af_unix stream sockets need to hold ref for pair sock"

This reverts commit 90d1f74c which is
commit bffdeaa8 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: I8f9ee72f8269598b93fe7abb14acd0d190242dcc
Signed-off-by: Greg Kroah-Hartman <gregkh@google.com>