This change removes support for subscribing to pending logs.
"Pending logs" were always an odd feature, because it can never be fully reliable. When support for it was added many years ago, the intention was for this to be used by wallet apps to show the 'potential future token balance' of accounts, i.e. as a way of notifying the user of incoming transfers before they were mined. In order to generate the pending logs, the node must pick a subset of all public mempool transactions, execute them in the EVM, and then dispatch the resulting logs to API consumers.
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