DOC: proxies: HAProxy only supports 3 connection modes

The 4th one (forceclose) has been deprecated and deleted from the
documentation in 10c6c16cde0b0b473a1ab16e958a7d6b61ed36fc

Signed-off-by: Julien Pivotto <roidelapluie@inuits.eu>
(cherry picked from commit 21ad31531601299eb52a56b50f90f491f46e4a88)
Signed-off-by: Willy Tarreau <w@1wt.eu>
(cherry picked from commit 0363fd302b8c48d86b7acb97e53c41cb58f6dd10)
Signed-off-by: Willy Tarreau <w@1wt.eu>
diff --git a/doc/configuration.txt b/doc/configuration.txt
index bda7217..06239a2 100644
--- a/doc/configuration.txt
+++ b/doc/configuration.txt
@@ -2333,7 +2333,7 @@
 
 In HTTP mode, the processing applied to requests and responses flowing over
 a connection depends in the combination of the frontend's HTTP options and
-the backend's. HAProxy supports 4 connection modes :
+the backend's. HAProxy supports 3 connection modes :
 
   - KAL : keep alive ("option http-keep-alive") which is the default mode : all
     requests and responses are processed, and connections remain open but idle