Make IWYU output in lint.cpp less messy

And re-run IWYU, adjust #includes.

src/complete.cpp

@@ -8,7 +8,6 @@
 #include <assert.h>
 #include <pthread.h>
 #include <pwd.h>
-#include <stdbool.h>
 #include <stddef.h>
 #include <wchar.h>
 #include <wctype.h>
@@ -20,6 +19,7 @@
 #include <string>
 #include <utility>
 
+
 #include "autoload.h"
 #include "builtin.h"
 #include "common.h"