Remove custom cache from `getBlockReceipts` method

[konstantinabl]

As a follow up of PR #3758, we need to remove the custom logic to retrieve a value from the cache. This is because top level RPC method eth_getBlockReceipts already caches its result.

See this discusssion https://github.com/hiero-ledger/hiero-json-rpc-relay/pull/3758/files#r2098146076 for more context.