[net] Remove CConnMan::SetAsmap()
[net] Remove CConnMan::SetAsmap()

Summary:
```
CAddrMan::m_asmap is now set directly in AppInitMain() so
CConnMan::SetAsmap() is no longer required.
```

Partial backport of [[https://github.com/bitcoin/bitcoin/pull/22791 | core#22791]]:
https://github.com/bitcoin/bitcoin/pull/22791/commits/593247872decd6d483a76e96d79433247226ad14

Depends on D12291.

Test Plan:
  ninja all check

Reviewers: #bitcoin_abc, PiRK

Reviewed By: #bitcoin_abc, PiRK

Differential Revision: https://reviews.bitcoinabc.org/D12292

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