Revert "ANDROID: GKI: net: add vendor hooks for 'struct nf_conn' lifecycle"

This reverts commit 995d95a7.

These hooks are never used, so remove them for now.

If they are needed by any real user, it can easily be reverted to add
them back and then the symbol should be added to the abi list at the
same time to prevent it from being removed again later.

Bug: 203756332
Bug: 171013716
Cc: Aditya Agrawal <aditya.a1@samsung.com>
Change-Id: Id1ddcded34c6fe2509e9a8be7b0f908b70915a0f
Signed-off-by: Greg Kroah-Hartman <gregkh@google.com>