Remove 'phonon' from the include directory
Summary:
Both the CMake and pkgconfig files say the include directory is
<prefix>/include/phonon4qt5. Only the .pri file points to a different location.
This fixes the nulloy build with recent phonon versions.
Reviewers: sitter, O4 phonon
Reviewed By: sitter, O4 phonon
Differential Revision: https://phabricator.kde.org/D23873