Revert "selftests/bpf: test for changing packet data from global functions"

This reverts commit 85a30a46 which is
commit 3f23ee55 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: I451125cd4bcf9152b13bbd536e74fab6e6fdbe9f
Signed-off-by: Greg Kroah-Hartman <gregkh@google.com>