[alias spec] Remove comment about refunds

Summary: This doesn't belong in the technical spec, even if there is an effort made to refund mistakes or duplicates, and can't be guaranteed.

Test Plan: Read it to make sure the info is correct

Reviewers: emack, bytesofman, #bitcoin_abc

Reviewed By: emack, #bitcoin_abc

Differential Revision: https://reviews.bitcoinabc.org/D13734