With events no longer being cached this is no longer needed.

Flushing the events cache worked by updating a recent number of rows in
the "events" table. This has the result that on PostgreSQL a lot of dead
tuples are produced on a regular basis. This in turn means that
PostgreSQL will spend considerable amounts of time vacuuming this table.
This in turn can lead to an increase of database load.

For GitLab.com we measured the impact of not using events caching and
found no measurable increase in response timings. Meanwhile not flushing
the events cache lead to the "events" table having no more dead tuples
as now rows are only inserted into this table.

As a result of this we are hereby removing events caching as it does not
appear to help and only increases database load.

For more information see the following comment:
https://gitlab.com/gitlab-org/gitlab-ce/merge_requests/6578#note_18864037

Hide project name in project activities

## What does this MR do?

- hide namespace and project name on project activity page

## Are there points in the code the reviewer needs to double check?

- did `.event_label` have any meaning?

## Why was this MR needed?

- all events on project activity page are from the same project, so the information was redundant

## What are the relevant issue numbers?

closes #18963

## Screenshots

### Before

![events-before](/uploads/76336e3f5cb08d4ef984df73c89aa90f/events-before.png)

### After

![events-after](/uploads/4a10718ed32960efc115d7854e5cad68/events-after.png)

![after-john-activity](/uploads/d9d151a829d8d32136525e8eb7ea04ad/after-john-activity.png)


See merge request !5068

Closes #17621