serializers/release: remove a redundant query
serializers/release: remove a redundant query

The `user_emails` would be evaluated twice. Once for resolving the set
of user_ids to be used in the `User` query, then once again when
iterating over down below.

gencer/sentry,looker/sentry,looker/sentry,mvaled/sentry,ifduyue/sentry,jean/sentry,gencer/sentry,beeftornado/sentry,mvaled/sentry,beeftornado/sentry,mvaled/sentry,jean/sentry,ifduyue/sentry,beeftornado/sentry,looker/sentry,mvaled/sentry,looker/sentry,gencer/sentry,mvaled/sentry,jean/sentry,ifduyue/sentry,looker/sentry,mvaled/sentry,jean/sentry,jean/sentry,gencer/sentry,ifduyue/sentry,gencer/sentry,ifduyue/sentry