Remove MaybeInfiniteInt::JustAfterMax

It was inherited from before half-open ranges, but it doesn't pull its
weight anymore. We lose a tiny bit of diagnostic precision.

compiler/rustc_pattern_analysis/src/rustc.rs

@@ -710,7 +710,7 @@ impl<'p, 'tcx: 'p> RustcMatchCheckCtxt<'p, 'tcx> {
                     None => PatRangeBoundary::PosInfinity,
                 }
             }
-            JustAfterMax | PosInfinity => PatRangeBoundary::PosInfinity,
+            PosInfinity => PatRangeBoundary::PosInfinity,
         }
     }