Some Logging Cleanup (#810)

* Remove unnecessary WPP definition.
* Various other small fixes.

tests/unit/test_platform.cpp

@@ -35,6 +35,7 @@
 
 #include <common/code_utils.hpp>
 #include <platform/alarm.h>
+#include <platform/logging.h>
 #include <platform/misc.h>
 #include <platform/radio.h>
 #include <platform/random.h>
@@ -305,6 +306,10 @@ exit:
         return kPlatResetReason_PowerOn;
     }
 
+    void otPlatLog(otLogLevel , otLogRegion , const char *, ...)
+    {
+    }
+
     //
     // Flash
     //