Remove incorrect assert

It's incorrect because `CtorSet::split` returns a non-present
constructor into `present` in one specific case: variable-length slices
of an empty type. That's because empty constructors of arity 0 break the
algorithm. This is a tricky corner case that's hard to do cleanly. The
assert wasn't adding much anyway.

compiler/rustc_pattern_analysis/src/lints.rs

@@ -94,12 +94,6 @@ impl<'p, 'tcx> PatternColumn<'p, 'tcx> {
                 column.expand_and_push(subpat);
             }
         }
-
-        assert!(
-            !specialized_columns[0].is_empty(),
-            "ctor {ctor:?} was listed as present but isn't;
-            there is an inconsistency between `Constructor::is_covered_by` and `ConstructorSet::split`"
-        );
         specialized_columns
     }
 }