Merge #9544: [trivial] Add end of namespace comments. Improve consistency.

Summary:
5a9b508 [trivial] Add end of namespace comments (practicalswift)

Tree-SHA512: 92b0fcae4d1d3f4da9e97569ae84ef2d6e09625a5815cd0e5f0eb6dd2ecba9852fa85c184c5ae9de5117050330ce995e9867b451fa8cd5512169025990541a2b

Backport of Core PR9544
https://github.com/bitcoin/bitcoin/pull/9544/files

Test Plan:

make check

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

Reviewed By: jasonbcox, O1 Bitcoin ABC, #bitcoin_abc, nakihito

Differential Revision: https://reviews.bitcoinabc.org/D3619