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

This reverts commit fa1fbb67 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: I0c2b1a2f4cd9a6c0095e8e7ac60ec65ef933881b
Signed-off-by: Greg Kroah-Hartman <gregkh@google.com>