[alias-server] Update getAliasInfoFromAlias to not return _id field

Summary:
T3060

User does not need this field and it complicates the unit tests for the API endpoint that will use this function. Remove.

Test Plan: npm test

Reviewers: #bitcoin_abc, Fabien

Reviewed By: #bitcoin_abc, Fabien

Subscribers: Fabien

Differential Revision: https://reviews.bitcoinabc.org/D14127