Remove unicap
    
    Upstream removed unicap support around 4.0 with this change
    
    commit 5869415a57524cf2dfb5eaba5aafa86ceb395d15 (HEAD)
    Author: Alexander Alekhin <alexander.alekhin@intel.com>
    Date:   Wed Nov 7 19:49:09 2018 +0300
    
        videoio: drop obsolete backends
    
        - VFW
        - QuickTime/QtKit
        - Unicap - GPL, no active support: https://github.com/unicap/unicap
        - DC1394 (1st version) / CMU1394
    
    So remove the configury and build requires for unicap.
    
    Reported-by: Robert Scheck <redhat-bugzilla@linuxnetz.de>
    Signed-off-by: Tom Rix <trix@redhat.com>