rtla: Fix build without libbpf header

rtla: Fix build without libbpf header

rtla supports building without libbpf. However, BPF actions
patchset [1] adds an include of bpf/libbpf.h into timerlat_bpf.h,
which breaks build on systems that don't have libbpf headers
installed.

This is a leftover from a draft version of the patchset where
timerlat_bpf_set_action() (which takes a struct bpf_program * argument)
was defined in the header. timerlat_bpf.c already includes bpf/libbpf.h
via timerlat.skel.h when libbpf is present.

Remove the redundant include to fix build on systems without libbpf
headers.

[1] https://lore.kernel.org/linux-trace-kernel/20251126144205.331954-1-tglozar@redhat.com/T/

Cc: John Kacur <jkacur@redhat.com>
Cc: Luis Goncalves <lgoncalv@redhat.com>
Cc: Crystal Wood <crwood@redhat.com>
Cc: Costa Shulyupin <costa.shul@redhat.com>
Link: https://patch.msgid.link/20260330091207.16184-1-tglozar@redhat.com
Reported-by: Steven Rostedt (Google) <rostedt@goodmis.org>
Closes: https://lore.kernel.org/linux-trace-kernel/20260329122202.65a8b575@robin/
Fixes: 8cd0f08ac72e ("rtla/timerlat: Support tail call from BPF program")
Signed-off-by: Tomas Glozar <tglozar@redhat.com>
Reviewed-by: Wander Lairson Costa <wander@redhat.com>
Signed-off-by: Steven Rostedt (Google) <rostedt@goodmis.org>