REORG: stkctr: move all the stick counters processing to stick-tables.c

Historically we used to have the stick counters processing put into
session.c which became stream.c. But a big part of it is now in
stick-table.c (eg: converters) but despite this we still have all
the sample fetch functions in stream.c

These parts do not depend on the stream anymore, so let's move the
remaining chunks to stick-table.c and have cleaner files.

What remains in stream.c is everything needed to attach/detach
trackers to the stream and to update the counters while the stream
is being processed.
diff --git a/include/proto/stick_table.h b/include/proto/stick_table.h
index 941e2ff..a5fd400 100644
--- a/include/proto/stick_table.h
+++ b/include/proto/stick_table.h
@@ -54,6 +54,8 @@
 struct stktable_key *stktable_fetch_key(struct stktable *t, struct proxy *px, struct session *sess,
                                         struct stream *strm, unsigned int opt,
                                         struct sample_expr *expr, struct sample *smp);
+struct stkctr *smp_fetch_sc_stkctr(struct session *sess, struct stream *strm, const struct arg *args, const char *kw);
+struct stkctr *smp_create_src_stkctr(struct session *sess, struct stream *strm, const struct arg *args, const char *kw);
 int stktable_compatible_sample(struct sample_expr *expr, unsigned long table_type);
 int stktable_register_data_store(int idx, const char *name, int std_type, int arg_type);
 int stktable_get_data_type(char *name);