Minor, remove TypeSystemContext.isNotNullNothing

Use equivalent isNothing instead

core/descriptors/src/org/jetbrains/kotlin/types/checker/ClassicTypeSystemContext.kt

@@ -261,11 +261,6 @@ interface ClassicTypeSystemContext : TypeSystemInferenceExtensionContext {
                 (constructor.declarationDescriptor != null || this is CapturedType || this is NewCapturedType || this is DefinitelyNotNullType || constructor is IntegerLiteralTypeConstructor)
     }
 
-    override fun KotlinTypeMarker.isNotNullNothing(): Boolean {
-        require(this is KotlinType, this::errorMessage)
-        return typeConstructor().isNothingConstructor() && !TypeUtils.isNullableType(this)
-    }
-
     override fun KotlinTypeMarker.contains(predicate: (KotlinTypeMarker) -> Boolean): Boolean {
         require(this is KotlinType, this::errorMessage)
         return containsInternal(this, predicate)

core/type-system/src/org/jetbrains/kotlin/types/AbstractTypeChecker.kt

@@ -538,7 +538,7 @@ object AbstractNullabilityChecker {
 
     fun AbstractTypeCheckerContext.hasPathByNotMarkedNullableNodes(start: SimpleTypeMarker, end: TypeConstructorMarker) =
         anySupertype(start, {
-            it.isNotNullNothing() || (!it.isMarkedNullable() && isEqualTypeConstructors(it.typeConstructor(), end))
+            it.isNothing() || (!it.isMarkedNullable() && isEqualTypeConstructors(it.typeConstructor(), end))
         }) {
             if (it.isMarkedNullable()) SupertypesPolicy.None else SupertypesPolicy.LowerIfFlexible
         }

core/type-system/src/org/jetbrains/kotlin/types/model/TypeSystemContext.kt

@@ -255,8 +255,6 @@ interface TypeSystemContext : TypeSystemOptimizationContext {
     fun TypeConstructorMarker.isAnyConstructor(): Boolean
     fun TypeConstructorMarker.isNothingConstructor(): Boolean
 
-    fun KotlinTypeMarker.isNotNullNothing(): Boolean
-
     /**
      *
      * SingleClassifierType is one of the following types: