Rollup merge of #119239 - compiler-errors:yield-coercion, r=davidtwco

Remove unnecessary arm in `check_expr_yield`

We always set up the `resume_yield_tys` for async blocks and fns, so this arm was unreachable.

compiler/rustc_hir/src/hir.rs

@@ -2110,12 +2110,6 @@ pub enum YieldSource {
     Yield,
 }
 
-impl YieldSource {
-    pub fn is_await(&self) -> bool {
-        matches!(self, YieldSource::Await { .. })
-    }
-}
-
 impl fmt::Display for YieldSource {
     fn fmt(&self, f: &mut fmt::Formatter<'_>) -> fmt::Result {
         f.write_str(match self {