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

This reverts commit 4ef54c6f.

The hooks have never been used, so they should be removed.  If they are
needed in the future, they can easily be added back.

Bug: 171013716
Cc: Vignesh Saravanaperumal <vignesh1.s@samsung.com>
Change-Id: I7dbdcc64b3de0d1a8266b09ab9991c212af79043
Signed-off-by: Greg Kroah-Hartman <gregkh@google.com>