MXS-2197 Remove most includes of maxscale/log.hh

All cc-files should include maxscale/ccdefs.hh, which includes
maxscale/log.hh. Consequently it need not be included again.

server/core/test/test_event.cc

@@ -21,7 +21,6 @@
 #include <iostream>
 #include <sstream>
 #include <maxbase/assert.h>
-#include <maxscale/log.hh>
 
 using namespace maxscale;
 using namespace std;