Inigo Martínez authored Oct 16, 2018 and Thomas Haller committed Dec 20, 2018

meson is able to get variables defined in pkg-config files such as
directory paths. PolicyKit defines in its pkg-config file the path to
the directory where `policy` files are present.

This removes the `polkit_dir` option to ease the move to start using
those variables. The `polkit` variable has also been converted to
boolean.

Fedora spec script has also been updated accordingly.