[gtk-doc] Copy makefile
[build] Fix EXTRA_DIST

I was under the impression that EXTRA_DISTs will happen regardless of
automake conditionals.  Apparently I was wrong.
[gtk-doc] Remove hack for deleting tmpl/

This was introduced in 029f46bde7e39094d3decb46525e91a97c5cc02c
and was in fact a bug in gtk-doc master:

  https://bugzilla.gnome.org/show_bug.cgi?id=707426