Doc: Remove unused image file (GH-8027)

(cherry picked from commit fe524df37cf3a8d4de291e7fc48257f96ff91bbe)
diff --git a/Doc/library/depgraph-output.png b/Doc/library/depgraph-output.png
deleted file mode 100644
index 960bb1b..0000000
--- a/Doc/library/depgraph-output.png
+++ /dev/null
Binary files differ