Auto merge of #131481 - nnethercote:rm-GenKillSet, r=cjgillot

Remove `GenKillAnalysis`

There are two kinds of dataflow analysis in the compiler: `Analysis`, which is the basic kind, and `GenKillAnalysis`, which is a more specialized kind for gen/kill analyses that is intended as an optimization. However, it turns out that `GenKillAnalysis` is actually a  pessimization! It's faster (and much simpler) to do all the gen/kill analyses via `Analysis`. This lets us remove `GenKillAnalysis`, and `GenKillSet`, and a few other things, and also merge `AnalysisDomain` into `Analysis`. The PR removes 500 lines of code and improves performance.

r? `@tmiasko`

clippy_utils/src/mir/possible_borrower.rs

@@ -213,7 +213,7 @@ impl<'b, 'tcx> PossibleBorrowerMap<'b, 'tcx> {
         self.bitset.0.clear();
         let maybe_live = &mut self.maybe_live;
         if let Some(bitset) = self.map.get(&borrowed) {
-            for b in bitset.iter().filter(move |b| maybe_live.contains(*b)) {
+            for b in bitset.iter().filter(move |b| maybe_live.get().contains(*b)) {
                 self.bitset.0.insert(b);
             }
         } else {
@@ -238,6 +238,6 @@ impl<'b, 'tcx> PossibleBorrowerMap<'b, 'tcx> {
 
     pub fn local_is_alive_at(&mut self, local: mir::Local, at: mir::Location) -> bool {
         self.maybe_live.seek_after_primary_effect(at);
-        self.maybe_live.contains(local)
+        self.maybe_live.get().contains(local)
     }
 }