Revert "[NI] Fix reporting smartcast diagnostics for intersection types"

This reverts commit 033d7262

That commit breaks bootstraping

core/descriptors/src/org/jetbrains/kotlin/types/TypeUtils.kt

@@ -243,12 +243,3 @@ val TypeParameterDescriptor.representativeUpperBound: KotlinType
         } ?: upperBounds.first()
     }
 
-fun KotlinType.expandIntersectionTypeIfNecessary(): Collection<KotlinType> {
-    if (constructor !is IntersectionTypeConstructor) return listOf(this)
-    val types = constructor.supertypes
-    return if (isMarkedNullable) {
-        types.map { it.makeNullable() }
-    } else {
-        types
-    }
-}