libbpf: Remove the duplicate checking of function storage

After the commit eac7d845 ("tools: libbpf: don't return '.text'
as a program for multi-function programs"), bpf_program__next()
in bpf_object__for_each_program skips the function storage such as .text,
so eliminate the duplicate checking.

Cc: Jakub Kicinski <jakub.kicinski@netronome.com>
Signed-off-by: Taeung Song <treeze.taeung@gmail.com>
Acked-by: Jakub Kicinski <jakub.kicinski@netronome.com>
Signed-off-by: Alexei Starovoitov <ast@kernel.org>