split out handler implementation from interface

Split out the handler object definition from the interface and drop the
default parameters.

Signed-off-by: Patrick Venture <venture@google.com>
Change-Id: Ie8c9dbf7881bbe6b5af3596a60430e3b3d573762
diff --git a/psu.hpp b/psu.hpp
index d2c5fbe..d45ce7f 100644
--- a/psu.hpp
+++ b/psu.hpp
@@ -18,8 +18,7 @@
 
 // Set a time-delayed PSU hard reset.
 ipmi_ret_t psuHardReset(const uint8_t* reqBuf, uint8_t* replyBuf,
-                        size_t* dataLen,
-                        const HandlerInterface* handler = &handlerImpl);
+                        size_t* dataLen, const HandlerInterface* handler);
 
 } // namespace ipmi
 } // namespace google