DecopeAsmap is a pure utility function and doesn't have any
dependencies on addrman, so move it to util/asmap.
Reviewer hint: use:
git diff --color-moved=dimmed-zebra --color-moved-ws=ignore-all-space
This is a backport of core#22911 [3/4]
https://github.com/bitcoin/bitcoin/pull/22911/commits/9fd5618610e91e3949536c5122cf31eb58c9aa6b
Depends on D10780