Summary:
We can't try to set or remove the sent label on gmail accounts because
the operation will silently fail and cause the threads to later bounce
back.
This occurred when trying to delete or archive a thread that contained a
sent message, and we incorrectly tried to overwrite or remove all of the
labels on messages, without regard for sent.
This was causing https://github.com/nylas/nylas-mail/issues/2706 and
sending and archiving to immediately bounce back.
Addresses T7757
Test Plan: unit tests
Reviewers: halla, evan, spang
Reviewed By: halla, evan, spang
Differential Revision: https://phab.nylas.com/D3829
