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.

compiler/fir/resolve/src/org/jetbrains/kotlin/fir/types/ConeInferenceContext.kt

@@ -25,8 +25,6 @@ interface ConeInferenceContext : TypeSystemInferenceExtensionContext, ConeTypeCo
 
     val symbolProvider: FirSymbolProvider get() = session.firSymbolProvider
 
-    override val isErrorTypeAllowed: Boolean get() = false
-
     override fun nullableNothingType(): SimpleTypeMarker {
         return session.builtinTypes.nullableNothingType.type//StandardClassIds.Nothing(symbolProvider).constructType(emptyArray(), true)
     }