Revert "net: tunnel: add pskb_inet_may_pull_reason() helper"

This reverts commit 74872113 which is
commit 7f20dbd7 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: Ia7fa3e33a9401b798259464174e35848b1fa91a7
Signed-off-by: Greg Kroah-Hartman <gregkh@google.com>