Drop log.h include from helpers.h

With the relocation of several functions, including inline functions,
from helpers to util, we no longer need to include log.h.  Which is a
good thing, since any subsystem that needs logging should explicitly
include log.h

Signed-off-by: Joachim Wiberg <troglobit@gmail.com>

plugins/tty.c

@@ -38,6 +38,7 @@
 #include "plugin.h"
 #include "service.h"
 #include "tty.h"
+#include "log.h"
 
 static void tty_watcher(void *arg, int fd, int events);