remove CRPCCommand constructor that takes rpcfn_type function pointer

Summary:
Remove the CRPCCommand arguments, now that they are asserted to be equal and thus redundant

Future work

• Removing all python regex linters on the args, now that RPCMan can be used to generate any output, including the cli.cpp table
• Auto-formatting and sanity checking the RPCExamples with RPCMan
• Checking passed-in json in self-check. Removing redundant checks
• Checking returned json against documentation to avoid regressions or false documentation
• Compile the RPC documentation at compile-time to ensure it doesn't change at runtime and is completely static

This concludes backport of core#18531
https://github.com/bitcoin/bitcoin/pull/18531/commits/faaf9c58e4aa809019d4ca12747dd47411988e37

Depends on D10743

Test Plan: ninja all check-all

Reviewers: #bitcoin_abc, Fabien

Reviewed By: #bitcoin_abc, Fabien

Differential Revision: https://reviews.bitcoinabc.org/D10744