file's sole purpose was to provide a dependency on pkg-config and set
some environment variables. Instead, turn pkg-config into a "tool"
in the tools framework, where the pkg-config wrapper automatically
adds PKG_CONFIG_LIBDIR to the environment before invoking the real
pkg-config.
For all package Makefiles that included pkg-config/buildlink3.mk, remove
that inclusion and replace it with USE_TOOLS+=pkg-config.
- aumix 2.8nb6, which only provides ncurses support. Note that its revision
is bumped to note the differences from the previous package.
- aumix-gtk 2.8, which includes GTK 2.x and ncurses support. While here,
add a missing build dependency on pkgconfig.
The descriptions have also been rewritten to note the differences.
Addresses PR pkg/27340.
