chore: delete unused util/network module

[kitlangton]

Summary

src/util/network.ts exports online() and proxied(). No file in packages/ imports either function or the module path.

Originally added with the proxy install fix (#12161) and touched by the TUI plugins refactor (#19347), but the callers have since moved on.

Test plan

• grep confirms zero importers of the module path
• grep confirms zero callers of online() or proxied() named exports
• CI green