Fixing more "Unused entity" warnings

Fixes:

/Users/sclay/projects/newsblur/clients/ios/Other Sources/Overshare Kit/OSKPagedHorizontalLayout.m:67:1: Ivar '_edgeInsets' which backs the property is not referenced in this property's accessor
/Users/sclay/projects/newsblur/clients/ios/Other Sources/Overshare Kit/OSKPagedHorizontalLayout.m:71:1: Ivar '_availableWidth' which backs the property is not referenced in this property's accessor
/Users/sclay/projects/newsblur/clients/ios/Other Sources/Overshare Kit/OSKPagedHorizontalLayout.m:76:1: Ivar '_availableHeight' which backs the property is not referenced in this property's accessor