Updated seed list for 0.19.6 release

Summary: Updating the mainnet seeds for 0.19.6. Testnet was skipped because my testnet seeder does not yet produce good results.

Test Plan: make check

Reviewers: deadalnix, Fabien, #bitcoin_abc

Reviewed By: Fabien, #bitcoin_abc

Differential Revision: https://reviews.bitcoinabc.org/D3036