selftests/bpf: Fix uprobe syscall shadow stack test

Now that we have uprobe syscall working properly with shadow stack,
we can remove testing limitations for shadow stack tests and make
sure uprobe gets properly optimized.

Signed-off-by: Jiri Olsa <jolsa@kernel.org>
Signed-off-by: Peter Zijlstra (Intel) <peterz@infradead.org>
Link: https://lkml.kernel.org/r/20250821141557.13233-1-jolsa@kernel.org