Inappropriate Downloading Notification. How to remove?
You need to clear the data and cache of the app:

The steps depend on phone make and Android version:

Touch and hold the notification > Touch the 'i', it will bring you to the app (Downloader Manager) > Clear Data and Cache and you're done.

On Samsung J5, Marshmallow (6.0.1)


Touching an app notification: 

Touching the i symbol:

Touching Storage option: