The generated settings-spec.xml should not be DIST-ed because it's
regenerated every time libnm-util changes. That meants it gets
rebuilt during 'make' even from a dist tarball. Thus, it shouldn't
be part of the dist tarball itself.
In addition, settings-spec.html shouldn't be included in
$(content_files) becuase this is added to EXTRA_DIST by gtk-doc.make.
Since generate-settings-spec.c the move from docs/api/ to tools/,
this started breaking distcheck even though the original Makefile
rules were wrong too.
a78d66bb38