Remove odd check for TypeFlags.NotUnionOrUnit

Author: ahejlsberg

src/compiler/checker.ts

@@ -21155,9 +21155,6 @@ namespace ts {
                             assumeTrue ? TypeFacts.EQUndefined : TypeFacts.NEUndefined;
                     return getTypeWithFacts(type, facts);
                 }
-                if (type.flags & TypeFlags.NotUnionOrUnit) {
-                    return type;
-                }
                 if (assumeTrue) {
                     const filterFn: (t: Type) => boolean = operator === SyntaxKind.EqualsEqualsToken ?
                         (t => areTypesComparable(t, valueType) || isCoercibleUnderDoubleEquals(t, valueType)) :

src/compiler/types.ts

@@ -4870,7 +4870,6 @@ namespace ts {
         // 'Narrowable' types are types where narrowing actually narrows.
         // This *should* be every type other than null, undefined, void, and never
         Narrowable = Any | Unknown | StructuredOrInstantiable | StringLike | NumberLike | BigIntLike | BooleanLike | ESSymbol | UniqueESSymbol | NonPrimitive,
-        NotUnionOrUnit = Any | Unknown | ESSymbol | Object | NonPrimitive,
         /* @internal */
         NotPrimitiveUnion = Any | Unknown | Enum | Void | Never | StructuredOrInstantiable,
         // The following flags are aggregated during union and intersection type construction