Revert "xfrm: Duplicate SPI Handling"

This reverts commit 94f39804.

It breaks CtsNetTestCases.IpSecManagerTunnelTest and a use-after-free
was reported upstream too [1]. Revert the patch until these problems are
addressed.

Bug: 439335971
Link: https://lore.kernel.org/all/CAJLDUOc6BFzUw0VE+TahCFVE7MZSvZNVao4JaenHXbg8BVKYqQ@mail.gmail.com/

 [1]
Change-Id: Iee95faa94348009a2ccd7ab5f4f6d4ea87afdbe8
Signed-off-by: Carlos Llamas <cmllamas@google.com>