selftests/bpf: Fix get_func_ip offset test for CONFIG_X86_KERNEL_IBT

selftests/bpf: Fix get_func_ip offset test for CONFIG_X86_KERNEL_IBT

With CONFIG_X86_KERNEL_IBT enabled the test for kprobe with offset
won't work because of the extra endbr instruction.

As suggested by Andrii adding CONFIG_X86_KERNEL_IBT detection
and using appropriate offset value based on that.

Also removing test7 program, because it does the same as test6.

Suggested-by: Andrii Nakryiko <andrii@kernel.org>
Acked-by: Andrii Nakryiko <andrii@kernel.org>
Signed-off-by: Jiri Olsa <jolsa@kernel.org>
Link: https://lore.kernel.org/r/20220926153340.1621984-7-jolsa@kernel.org
Signed-off-by: Alexei Starovoitov <ast@kernel.org>