MINOR: http: status 301 should not be marked non-cacheable

Also, browsers behaviour is inconsistent regarding the Cache-Control
header field on a 301.
diff --git a/src/proto_http.c b/src/proto_http.c
index 24e0a76..b85c6aa 100644
--- a/src/proto_http.c
+++ b/src/proto_http.c
@@ -75,7 +75,6 @@
 /* Warning: no "connection" header is provided with the 3xx messages below */
 const char *HTTP_301 =
 	"HTTP/1.1 301 Moved Permanently\r\n"
-	"Cache-Control: no-cache\r\n"
 	"Content-length: 0\r\n"
 	"Location: "; /* not terminated since it will be concatenated with the URL */