Revert "selftests/bpf: Fix "dubious pointer arithmetic" test"

This reverts commit 6098562e.
It shouldn't be in v5.4 because the commit it fixes is only present in
v5.9 onward.

Signed-off-by: Jean-Philippe Brucker <jean-philippe@linaro.org>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>