Reinstalling a content pack doesn't restore messages

The problem I encounter is that if I uninstall and then reinstall the same content pack, messages are not preserved while this used to be the case IIRC.

## Expected Behavior
I expect that messages would be reassigned to their dedicated stream when reinstalling the content pack.

## Current Behavior
The streams are recreated empty.
The index still contains the messages.

## Steps to Reproduce (for bugs)
1. Install your content pack (which defines a stream)
2. Have logs available in that stream
3. Uninstall the content pack
4. Reinstall the same content pack
5. Check the stream content

## Context
We have a postman collection that we use for configuring Graylog through its API. One of the operations is to remove the current content pack and install the new one. Doing this in production now means that we will not be able to access anterior logs anymore.

## Your Environment
* Graylog Version: graylog/graylog:3.0.2
* Elasticsearch Version: docker.elastic.co/elasticsearch/elasticsearch-oss:6.8.1
* MongoDB Version: mongo:3.6.13
* Operating System: Debian
* Browser version: Firefox 72.0.1