Rollup merge of rust-lang#74227 - erikdesjardins:layun, r=estebank

Remove an unwrap in layout computation

A tiny improvement.

src/librustc_middle/ty/layout.rs

@@ -774,12 +774,12 @@ impl<'tcx> LayoutCx<'tcx, TyCtxt<'tcx>> {
                     (present_variants.next(), present_variants.next())
                 };
                 let present_first = match present_first {
-                    present_first @ Some(_) => present_first,
+                    Some(present_first) => present_first,
                     // Uninhabited because it has no variants, or only absent ones.
                     None if def.is_enum() => return tcx.layout_raw(param_env.and(tcx.types.never)),
                     // If it's a struct, still compute a layout so that we can still compute the
                     // field offsets.
-                    None => Some(VariantIdx::new(0)),
+                    None => VariantIdx::new(0),
                 };
 
                 let is_struct = !def.is_enum() ||
@@ -791,7 +791,7 @@ impl<'tcx> LayoutCx<'tcx, TyCtxt<'tcx>> {
                     // Struct, or univariant enum equivalent to a struct.
                     // (Typechecking will reject discriminant-sizing attrs.)
 
-                    let v = present_first.unwrap();
+                    let v = present_first;
                     let kind = if def.is_enum() || variants[v].is_empty() {
                         StructKind::AlwaysSized
                     } else {