remove include boost/asio.hpp

This makes it possible to build without including asio.hpp. This should
reduce build times and makes it more explicit what parts of asio are
getting used.

Tested: builds as expected

Change-Id: Ibfdf1c3f842a8a86ef45ead3c964c51422ffd673
Signed-off-by: Vernon Mauery <vernon.mauery@linux.intel.com>
diff --git a/libipmid/sdbus-asio.cpp b/libipmid/sdbus-asio.cpp
index e505797..fb71805 100644
--- a/libipmid/sdbus-asio.cpp
+++ b/libipmid/sdbus-asio.cpp
@@ -1,4 +1,4 @@
-#include <boost/asio.hpp>
+#include <boost/asio/io_context.hpp>
 #include <memory>
 #include <sdbusplus/asio/connection.hpp>