Fix compilation on Kotlin/Native

[Mr3zee]

Subsystem
Compiler plugin

Problem Description
Compilation on Kotlin/Native targets produces wrong IR, leading to

kotlinx.serialization.SerializationException: Serializer for class 'rpcMethod' is not found.
Please ensure that class is marked as '@Serializable' and that the serialization compiler plugin is applied.
To get enum serializer on Kotlin/Native, it should be annotated with @Serializable annotation.
To get interface serializer on Kotlin/Native, use PolymorphicSerializer() constructor function.

Solution
Remove supertype overriding for rpcMethod classes, fixing the issue