Make figs includable in main document

Remove the capability to build them as standalone document but we can
include them in the main document.  It should simplify things down the
road.

book/figures/fig-stiff-starter-conversion.tex

@@ -1,6 +1,3 @@
-\input{./vars}
-
-\begin{document}
 \begin{tikzpicture}[node distance = 3cm, auto]
   \node [block] (init) {\footnotesize Make a regular or liquid starter};
   \node [block, right of=init] (feed_new_ratio) {\footnotesize Mix 10g existing starter, 50g flour and 25g water};
@@ -26,4 +23,3 @@
   \path [line] (too_dry) -- node{\footnotesize yes} (add_water);
   \path [line] (ready_signs) -- node{\footnotesize yes} (last_feed);
 \end{tikzpicture}
-\end{document}