remove unneeded includes of core_io.h and network.h

Summary:
D9603 remove the need to include core_io.h in a few files

D9665 and D9107 removed the need to include network.h in most files. This is now used only in one place after this commit, so we can look into removing network.{h|cpp} altogether (in a separate commit).

Test Plan: ninja all check-all

Reviewers: #bitcoin_abc, sdulfari

Reviewed By: #bitcoin_abc, sdulfari

Differential Revision: https://reviews.bitcoinabc.org/D11563