In confirm close dialog, remove 'close current tab' option

Summary:
When there is only one tab and a process is running, remove the
'close current tab' option when attempting to close Konsole.

Test Plan:
1. Open Konsole (assuming you have not check 'Do not ask again')
2. Start any process (ie top)
3.  Try to close Konsole

Should only be 2 options,  'Close window' and 'Cancel'

Reviewers: #konsole, hindenburg

Reviewed By: #konsole, hindenburg

Subscribers: hindenburg, ngraham, konsole-devel

Tags: #konsole

Differential Revision: https://phabricator.kde.org/D23146