aya-ebpf: Remove irrelevant `FIXME` comment

eBPF verifier in recent kernels should be smart enough to track map
map types and catch invalid pointer casts. Rust type system makes sure
that the `get` method can return only the same type the map was created
with. Therefore, safe usage of Aya map types shouldn't cause element
type mismatches.

Manual alignment checks (`pointer::is_aligned` or manual pointer
arithmetic operations) cause the following verifier error:

```
bitwise operator &= on pointer prohibited
```

And it extremely unlikely `bpf_map_lookup_elem` ever returns a
misaligned pointer.

ebpf/aya-ebpf/src/maps/array.rs

@@ -49,7 +49,6 @@ impl<T> Array<T> {
 
     #[inline(always)]
     pub fn get(&self, index: u32) -> Option<&T> {
-        // FIXME: alignment
         unsafe { self.lookup(index).map(|p| p.as_ref()) }
     }