DOC: cfgparse: Warn on option (tcp|http)log in backend

The option does not seem to have any effect since at least haproxy
1.3. Also the `log-format` directive already warns when being used
in a backend.
diff --git a/doc/configuration.txt b/doc/configuration.txt
index 7cc5c13..51a1493 100644
--- a/doc/configuration.txt
+++ b/doc/configuration.txt
@@ -6071,7 +6071,7 @@
 option httplog [ clf ]
   Enable logging of HTTP request, session state and timers
   May be used in sections :   defaults | frontend | listen | backend
-                                 yes   |    yes   |   yes  |   yes
+                                 yes   |    yes   |   yes  |   no
   Arguments :
     clf       if the "clf" argument is added, then the output format will be
               the CLF format instead of HAProxy's default HTTP format. You can
@@ -6087,8 +6087,6 @@
   frontend, backend and server name, and of course the source address and
   ports.
 
-  This option may be set either in the frontend or the backend.
-
   Specifying only "option httplog" will automatically clear the 'clf' mode
   if it was set by default.
 
@@ -6938,7 +6936,7 @@
 option tcplog
   Enable advanced logging of TCP connections with session state and timers
   May be used in sections :   defaults | frontend | listen | backend
-                                 yes   |    yes   |   yes  |   yes
+                                 yes   |    yes   |   yes  |   no
   Arguments : none
 
   By default, the log output format is very poor, as it only contains the
@@ -6950,8 +6948,6 @@
   find which of the client or server disconnects or times out. For normal HTTP
   proxies, it's better to use "option httplog" which is even more complete.
 
-  This option may be set either in the frontend or the backend.
-
   "option tcplog" overrides any previous "log-format" directive.
 
   See also :  "option httplog", and section 8 about logging.