macro_optional_find_package -> find_package in 3.0

[Jaroslaw Staniek]

Hi,
I propose to remove usage of macro_optional_find_package() and just
using find_package().
See https://blogs.kde.org/2011/11/11/cool-new-stuff-cmake-286-3-standard-way-disable-optional-packages

-- 
regards, Jaroslaw Staniek

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