Drop isErrorTypeAllowed flag from type system context

The flag was used exclusively during calculation of common super type.
This change relies on assumption, that common super type is
NOT calculated in IR type system context.

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

@@ -33,8 +33,6 @@ import kotlin.contracts.ExperimentalContracts
 import kotlin.contracts.contract
 
 interface ClassicTypeSystemContext : TypeSystemInferenceExtensionContext, TypeSystemCommonBackendContext {
-    override val isErrorTypeAllowed: Boolean get() = false
-
     override fun TypeConstructorMarker.isDenotable(): Boolean {
         require(this is TypeConstructor, this::errorMessage)
         return this.isDenotable