Remove admonition style. Let the CSS do the styling.

Always have admonition graphics


[SVN r33450]

tools/boostbook

@@ -1 +1 @@
-Subproject commit 0f83dbdf6f1a00a1f33c1d99f49fc8d9ecb21e0b
+Subproject commit 570f95bbcb51833b546209e7e2c189ee92d5250d