RPC: Rephrase generatetoaddress help, and use PACKAGE_NAME
RPC: Rephrase generatetoaddress help, and use PACKAGE_NAME

Summary: This is a backport of [[https://github.com/bitcoin/bitcoin/pull/19282 | core#19282]]

Test Plan: `src/bitcoin-cli help generatetoaddress`

Reviewers: #bitcoin_abc, Fabien, deadalnix

Reviewed By: #bitcoin_abc, Fabien, deadalnix

Subscribers: Fabien

Differential Revision: https://reviews.bitcoinabc.org/D9615

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