travis: Remove unused sudo:false

Summary:
This is a backport of secp256k1 PR606

Note that we already removed the sudo:false in a previous patch, so this is mostly to fix discrepencies that would cause unecessary merge conflicts.

Test Plan: Travis will tell us if it's unhappy. I simply assume it won't.

Reviewers: #bitcoin_abc, Fabien

Reviewed By: #bitcoin_abc, Fabien

Subscribers: Fabien

Differential Revision: https://reviews.bitcoinabc.org/D4990