Remove uses of ResultsClonedCursor.

By just cloning the entire `Results` in the one place where
`ResultsClonedCursor` was used. This is extra allocations but the
performance effect is negligible.

compiler/rustc_mir_dataflow/src/lib.rs

@@ -24,7 +24,7 @@ pub use self::framework::{
     fmt, lattice, visit_results, Analysis, AnalysisDomain, Direction, GenKill, GenKillAnalysis,
     JoinSemiLattice, MaybeReachable, Results, ResultsCursor, ResultsVisitable, ResultsVisitor,
 };
-use self::framework::{Backward, ResultsClonedCursor, SwitchIntEdgeEffects};
+use self::framework::{Backward, SwitchIntEdgeEffects};
 use self::move_paths::MoveData;
 
 pub mod debuginfo;