Remove yellow code (#2691)

The corresponding change in the compiler (see KT-67764) improves the detection
of `CONFLICTING_PROJECTIONS`, which makes this code yellow, because now it provokes
`REDUNDANT_PROJECTION`.

^KT-67764
^KT-68488

Author: lunakoly

core/commonMain/src/kotlinx/serialization/modules/SerializersModule.kt

@@ -208,7 +208,7 @@ internal class SerialModuleImpl(
         }
 
         polyBase2DefaultDeserializerProvider.forEach { (baseClass, provider) ->
-            collector.polymorphicDefaultDeserializer(baseClass as KClass<Any>, provider as (PolymorphicDeserializerProvider<out Any>))
+            collector.polymorphicDefaultDeserializer(baseClass as KClass<Any>, provider as (PolymorphicDeserializerProvider<Any>))
         }
     }
 }