Remove superfluous config example from eviction content

https://infinispan.org/docs/stable/titles/configuring/configuring.html#custom_class_eviction-config

Remove the following section from the configuration guide:

Custom Classes with Memory-Based Eviction

You must use binary or off-heap storage memory based eviction, as in the following examples:
Declarative configuration

<!-- Enable memory based eviction with 1 GB/> -->
<memory>
<binary size="1000000000" eviction="MEMORY"/>
</memory>

Programmatic configuration

Configuration c = new ConfigurationBuilder()
.memory()
.storageType(StorageType.BINARY)
.evictionType(EvictionType.MEMORY)
.size(1_000_000_000)
.build();