Remove SwitchIntTarget.

It's only passed to `Analysis::apply_switch_int_edge_effect`, and the
existing impls of that method only use the `value` field. So pass that
instead.

compiler/rustc_mir_dataflow/src/framework/mod.rs

@@ -222,7 +222,7 @@ pub trait Analysis<'tcx> {
         &mut self,
         _data: &mut Self::SwitchIntData,
         _state: &mut Self::Domain,
-        _edge: SwitchIntTarget,
+        _value: SwitchTargetValue,
     ) {
         unreachable!();
     }
@@ -432,10 +432,5 @@ impl EffectIndex {
     }
 }
 
-pub struct SwitchIntTarget {
-    pub value: SwitchTargetValue,
-    pub target: BasicBlock,
-}
-
 #[cfg(test)]
 mod tests;