tools: bpf: fix BTF code added twice to different trees

commit 38d5d3b3 ("bpf: Introduce BPF_ANNOTATE_KV_PAIR")

added to the bpf and net trees what

commit 92b57121 ("bpf: btf: export btf types and name by offset from lib")

has already added to bpf-next/net-next, but in slightly different
location.  Remove the duplicates (to fix build of libbpf).

Signed-off-by: Jakub Kicinski <jakub.kicinski@netronome.com>
Signed-off-by: David S. Miller <davem@davemloft.net>