Remove unused PlaceContext::NonUse(NonUseContext::Coverage)

compiler/rustc_middle/src/mir/visit.rs

@@ -1150,8 +1150,6 @@ pub enum NonUseContext {
     StorageDead,
     /// User type annotation assertions for NLL.
     AscribeUserTy,
-    /// Coverage code region and counter metadata.
-    Coverage,
     /// The data of an user variable, for debug info.
     VarDebugInfo,
 }

compiler/rustc_mir/src/borrow_check/def_use.rs

@@ -72,8 +72,7 @@ pub fn categorize(context: PlaceContext) -> Option<DefUse> {
         PlaceContext::MutatingUse(MutatingUseContext::Drop) =>
             Some(DefUse::Drop),
 
-        // Coverage and debug info are neither def nor use.
-        PlaceContext::NonUse(NonUseContext::Coverage) |
+        // Debug info is neither def nor use.
         PlaceContext::NonUse(NonUseContext::VarDebugInfo) => None,
     }
 }

compiler/rustc_mir/src/dataflow/impls/init_locals.rs

@@ -97,7 +97,6 @@ fn visit_local(&mut self, &local: &Local, context: PlaceContext, _: Location) {
             PlaceContext::NonUse(
                 NonUseContext::StorageLive
                 | NonUseContext::AscribeUserTy
-                | NonUseContext::Coverage
                 | NonUseContext::VarDebugInfo,
             )
             | PlaceContext::NonMutatingUse(