Currently kpackage_install_package fails if KDE_INSTALL_DIRS_NO_DEPRECATED
is set to TRUE, because the macro is still using the deprecated var
DATA_INSTALL_DIR
It should be fine to bump the min version of ECM required to needed ECM 1.6.0,
as someone using KF5 5.27 very surely also has a similar recent ECM.
(Compare also recent similar patch for KF5PackageMacros.cmake)
Also done (will be separate commits)
- remove unused variable KPACKAGE_DATA_INSTALL_DIR
- fix api dox for default value of install_dir