DOC: Update http-buffer-request description to remove the part about chunks

The limitation on the first chunk for chunked requests was true for the legacy
HTTP mode. But, it does not exist with the HTX. Becaue, the legacy HTTP mode was
removed in 2.1, this limitation does not exist anymore.
diff --git a/doc/configuration.txt b/doc/configuration.txt
index b17ab90..463d172 100644
--- a/doc/configuration.txt
+++ b/doc/configuration.txt
@@ -6235,11 +6235,10 @@
   connecting to the server. Another use case consists in taking the routing
   decision based on the request body's contents. This option placed in a
   frontend or backend forces the HTTP processing to wait until either the whole
-  body is received, or the request buffer is full, or the first chunk is
-  complete in case of chunked encoding. It can have undesired side effects with
-  some applications abusing HTTP by expecting unbuffered transmissions between
-  the frontend and the backend, so this should definitely not be used by
-  default.
+  body is received or the request buffer is full. It can have undesired side
+  effects with some applications abusing HTTP by expecting unbuffered
+  transmissions between the frontend and the backend, so this should definitely
+  not be used by default.
 
   See also : "option http-no-delay", "timeout http-request"