http.c: Rely on select instead of tracking whether data was received

Since now select is used with the file descriptors of the http connections,
tracking whether data was received recently (and trying to read more in
that case) is no longer necessary. Instead, always call select and rely on
it to return as soon as new data can be read.

Signed-off-by: Mika Fischer <mika.fischer@zoopnet.de>
Helped-by: Jeff King <peff@peff.net>
Signed-off-by: Junio C Hamano <gitster@pobox.com>

http.h

@@ -89,7 +89,6 @@ extern void step_active_slots(void);
 extern void http_init(struct remote *remote);
 extern void http_cleanup(void);
 
-extern int data_received;
 extern int active_requests;
 extern int http_is_verbose;
 extern size_t http_post_buffer;