Remove FIXME from MIR always_storage_live_locals

compiler/rustc_mir_dataflow/src/storage.rs

@@ -4,9 +4,6 @@ use rustc_middle::mir::{self, Local};
 /// The set of locals in a MIR body that do not have `StorageLive`/`StorageDead` annotations.
 ///
 /// These locals have fixed storage for the duration of the body.
-//
-// FIXME: Currently, we need to traverse the entire MIR to compute this. We should instead store it
-// as a field in the `LocalDecl` for each `Local`.
 pub fn always_storage_live_locals(body: &mir::Body<'_>) -> BitSet<Local> {
     let mut always_live_locals = BitSet::new_filled(body.local_decls.len());