py: Clean up includes.

Remove unnecessary includes. Add includes that improve portability.
diff --git a/py/parse.c b/py/parse.c
index a7b73a5..1381f12 100644
--- a/py/parse.c
+++ b/py/parse.c
@@ -1,9 +1,6 @@
-#include <unistd.h>
-#include <stdlib.h>
+#include <stdbool.h>
 #include <stdint.h>
 #include <stdio.h>
-#include <ctype.h>
-#include <string.h>
 #include <assert.h>
 
 #include "misc.h"