doc: Fix typo in Coin doxygen comment

Summary:
CTxOutCompressor has been renamed in D8632, so rename it in the docs as well.

This is a backport of Core PR18854

Test Plan:

$ grep -r TxOutCompression src/ | wc -l
8
$ grep -r CTxOutCompressor src/ | wc -l
0

Reviewers: #bitcoin_abc, majcosta

Reviewed By: #bitcoin_abc, majcosta

Differential Revision: https://reviews.bitcoinabc.org/D9080