Merge #10728: fix typo in help text for removeprunedfunds

Summary:
ecb4fc382 fix typo in help text for removeprunedfunds (Akio Nakamura)

Tree-SHA512: 2603851f1ac90bc0b90ced6355b0056e4cb658303cb2cd03ee0827ed0053157ebb87de48076f4d4f556991bfdbdb65d0a68a8dbd275c501cee4c9b5746a9562b

Backport of Core PR10728
https://github.com/bitcoin/bitcoin/pull/10728/

Test Plan:

make check
./bitcoind
./bitcoin-cli help removeprunedfunds

removeprunedfunds should be spelled correctly in examples.

Reviewers: deadalnix, Fabien, jasonbcox, markblundeberg, O1 Bitcoin ABC, #bitcoin_abc

Reviewed By: deadalnix, O1 Bitcoin ABC, #bitcoin_abc

Differential Revision: https://reviews.bitcoinabc.org/D3623