Sanitize RemoteEmail user prop (#27170)

* Sanitize RemoteEmail user prop

If the server is configured to hide user emails, the "RemoteEmail"
user property will be sanitized as well, effectively hiding the real
email of remote users.

* fix merge conflict

---------

Co-authored-by: Doug Lauder <wiggin77@warpmail.net>
Co-authored-by: Mattermost Build <build@mattermost.com>

server/platform/services/sharedchannel/service.go

@@ -30,8 +30,6 @@ const (
 	NotifyMinimumDelay           = time.Second * 2
 	MaxUpsertRetries             = 25
 	ProfileImageSyncTimeout      = time.Second * 5
-	KeyRemoteUsername            = "RemoteUsername"
-	KeyRemoteEmail               = "RemoteEmail"
 )
 
 // Mocks can be re-generated with `make sharedchannel-mocks`.