fix: remove collective name from expense email

[nosro]

As per https://github.com/opencollective/opencollective/issues/5207 the expense email comment notification goes to both the admin as well as the expense payee, so a singular greeting name doesn't work.

As a quick fix, remove the greeting name to make the email greeting generic for both recipients.

[nosro]

I'm unclear if one or two templates are involved: collective.comment.created.hbs and/or expense.comment.created.hbs. I will look further to spot the contexts these are used. Maybe a different greeting name can be set in each.

I can see that there are separate notifications for three recipients potentially: admin of the collective, admin of the host, and author of the expense: https://github.com/opencollective/opencollective-api/blob/main/server/lib/notifications/email.ts#L304-L326

A better fix would be to have a separate email template fragment for each recipient to allow for different greeting names, or even better - a recipient name set in the template data to make a single template do the job.