Changes to message processor configuration will pop duplicate toasts

## Expected Behavior

Notifications should not be duplicated

## Current Behavior

When enabling or disabling a message processor, the notification toast is raised twice.

## Steps to Reproduce (for bugs)

1. Go to system/configurations/message processor
2. Disable a checkbox
3. Observe duplicate toasts

## Context

Distracting and doesn't inspire confidence in the quality of the system

## Your Environment

* Graylog Version: 6.2, 6.3, 7.0