MEDIUM: sample change the prototype of sample-fetches and converters functions

This patch removes the structs "session", "stream" and "proxy" from
the sample-fetches and converters function prototypes.

This permits to remove some weight in the prototype call.
diff --git a/src/map.c b/src/map.c
index eea3f4f..a75605c 100644
--- a/src/map.c
+++ b/src/map.c
@@ -164,8 +164,7 @@
 	return 1;
 }
 
-static int sample_conv_map(struct stream *stream, const struct arg *arg_p,
-                           struct sample *smp, void *private)
+static int sample_conv_map(const struct arg *arg_p, struct sample *smp, void *private)
 {
 	struct map_descriptor *desc;
 	struct pattern *pat;