sdbusplus: use shorter type aliases

The sdbusplus headers provide shortened aliases for many types.
Switch to using them to provide better code clarity and shorter
lines.  Possible replacements are for:
  * bus_t
  * exception_t
  * manager_t
  * match_t
  * message_t
  * object_t
  * slot_t

Change-Id: Id13cf695f25312a9561c0954f5ed133985ab1222
Signed-off-by: Patrick Williams <patrick@stwcx.xyz>
diff --git a/include/user_monitor.hpp b/include/user_monitor.hpp
index bd8ed24..73f6303 100644
--- a/include/user_monitor.hpp
+++ b/include/user_monitor.hpp
@@ -9,7 +9,7 @@
 namespace bmcweb
 {
 
-inline void onUserRemoved(sdbusplus::message::message& msg)
+inline void onUserRemoved(sdbusplus::message_t& msg)
 {
     sdbusplus::message::object_path p;
     msg.read(p);