Deprecated code checking with backup

[sugaroverflow]

Debugging a site clone issue with @sewmyheadon got us this notice:

Undefined index 'backup' /SiteCloneCommand/php on Line 117 of SiteCloneCommand

It appears that we have some code from the previous version of the the site:clone plugin. 2.0.0 brought about separating the backup options into source and destination.

Opening this issue to determine if we'd like to keep this functionality and if so, for both backup options to to remove it.