MEDIUM: proxy: remove acl_requires and just keep a flag "http_needed"

Proxy's acl_requires was a copy of all bits taken from ACLs, but we'll
get rid of ACL flags and only rely on sample fetches soon. The proxy's
acl_requires was only used to allocate an HTTP context when needed, and
was even forced in HTTP mode. So better have a flag which exactly says
what it's supposed to be used for.
diff --git a/src/log.c b/src/log.c
index 25dda04..165fd72 100644
--- a/src/log.c
+++ b/src/log.c
@@ -347,8 +347,7 @@
 
 	/* check if we need to allocate an hdr_idx struct for HTTP parsing */
 	/* Note, we may also need to set curpx->to_log with certain fetches */
-	if (expr->fetch->use & SMP_USE_HTTP_ANY)
-		curpx->acl_requires |= ACL_USE_L7_ANY;
+	curpx->http_needed |= !!(expr->fetch->use & SMP_USE_HTTP_ANY);
 
 	/* FIXME: temporary workaround for missing LW_XPRT flag needed with some
 	 * sample fetches (eg: ssl*). We always set it for now on, but this will