All you need to run is:
Remove-MailboxFolderPermission -Identity "sharedmailbox@contoso.com:\calendar" -user user1@contoso.com
Remove-MailboxFolderPermission -Identity kim@contoso.com:\Training -User john@contoso.com
You can't use this cmdlet to selectively remove permissions from a user on a mailbox folder. The cmdlet removes all permissions that are assigned to the user on the specified folder. To modify the permissions that are assigned to the user on a mailbox folder, use the Set-MailboxFolderPermission cmdlet.