REORG: include: move channel.h to haproxy/channel{,-t}.h

The files were moved with no change. The callers were cleaned up a bit
and a few of them had channel.h removed since not needed.
diff --git a/src/cfgparse.c b/src/cfgparse.c
index 429954c..15f768e 100644
--- a/src/cfgparse.c
+++ b/src/cfgparse.c
@@ -39,6 +39,7 @@
 #include <haproxy/api.h>
 #include <haproxy/capture.h>
 #include <common/cfgparse.h>
+#include <haproxy/channel.h>
 #include <haproxy/check.h>
 #include <haproxy/chunk.h>
 #include <haproxy/connection.h>
@@ -69,7 +70,6 @@
 #include <haproxy/global.h>
 
 #include <proto/backend.h>
-#include <proto/channel.h>
 #include <proto/filters.h>
 #include <proto/log.h>
 #include <haproxy/protocol.h>