Remove filtering by pending blocks

[kclowes]

What feature should we add?

Geth has removed the ability to filter by pending blocks. Reasoning from Geth 1.14.0 release notes here:

We see next to no value in monitoring the logs of a random subset of transactions that might (but probably mostly will not) end up in the next block. Power users who wish to monitor the transaction pool for MEV (or similar) purposes, should hook into Geth directly and extract the exact data they need, rather than rely on insufficient API endpoints.

I think we can fairly safely remove it too. TBD if this needs to go in v7 before breaking changes are wrapped.

[pacrob]

Seems like this should be considered breaking, even if the endpoint isn't actually that useful. Adding to v8 stuff.