samples/bpf: Remove unused test_ipip.sh

samples/bpf: Remove unused test_ipip.sh

The tcbpf2_kern.o and related kernel sections are moved to bpf
selftest folder since b05cd7404323 ("samples/bpf: remove the bpf tunnel
testsuite."). Remove this one as well.

Fixes: b05cd7404323 ("samples/bpf: remove the bpf tunnel testsuite.")
Signed-off-by: Hangbin Liu <liuhangbin@gmail.com>
Signed-off-by: Alexei Starovoitov <ast@kernel.org>
Acked-by: Martin KaFai Lau <kafai@fb.com>
Link: https://lore.kernel.org/bpf/20201110015013.1570716-3-liuhangbin@gmail.com