shell/Windows: Remove the UPDATE_VIEW message handling

shell/Windows: Remove the UPDATE_VIEW message handling

The client now tries to only push STATUS messages to connections
unless they previously requested it with a RETRIEVE_FILE_STATUS,
but this means that we now have to make sure that a new connection
will rerequest every icon that the user will see on files from that
point on.

To that end, we now send a SHChangeNotify for every file in the cache
when we lose the connection (or on UNREGISTER_PATH) to make sure that
what's on the screen matches what's in the cache. We also remove the
_oldCache logic that made this more difficult to enforce.

The client has been able to reliably push status updates on macOS
for a few versions now, and we don't need it on Windows either. The
_oldCache mechanism was to avoid sending to many update requests
when receiving an UPDATE_VIEW.

Also fixes #4766