Listeners map not cleared when device is disconnected

[paulvarache]

Scenario:

• Discover device x
• Connect
• Subscribe to characteristic c in service s
• Connection drops
• Discover device x again
• Connect to device x again
• Subscribe to characteristic c in service s again
• Callback is never called

It seems noble-uwp caches the listener attached to a subscription and do not call the nodert library to subscribe to it again, but doesn't clear this cache once a device is disconnected.