Migrate seeder to use node's sleep utility function

Summary:
UninterruptibleSleep already provides a way to use std::chrono::duration.
This patch improves code readability and make changes in D10666 less error prone by
removing seeder's Sleep in favor of UninterruptibleSleep that the node uses.

Test Plan:

ninja check-seeder bitcoin-seeder
./src/seeder/bitcoin-seeder

Examine output in dnsseed.dump. Use ls -al to verify dump is occurring at expected intervals.

Reviewers: O1 Bitcoin ABC, #bitcoin_abc, Fabien

Reviewed By: O1 Bitcoin ABC, #bitcoin_abc, Fabien

Subscribers: Fabien

Differential Revision: https://reviews.bitcoinabc.org/D11119