MAJOR: config: remove the deprecated reqsetbe / reqisetbe actions

These ones were already obsoleted in 1.4, marked for removal in 1.5,
and not documented anymore. They used to emit warnings, and do still
require quite some code to stay in place. Let's remove them now.
diff --git a/doc/configuration.txt b/doc/configuration.txt
index a2eac7b..fdb0ddc 100644
--- a/doc/configuration.txt
+++ b/doc/configuration.txt
@@ -1608,12 +1608,10 @@
 reqideny                                  -          X         X         X
 reqipass                                  -          X         X         X
 reqirep                                   -          X         X         X
-reqisetbe                                 -          X         X         X
 reqitarpit                                -          X         X         X
 reqpass                                   -          X         X         X
 reqrep                                    -          X         X         X
 -- keyword -------------------------- defaults - frontend - listen -- backend -
-reqsetbe                                  -          X         X         X
 reqtarpit                                 -          X         X         X
 retries                                   X          -         X         X
 rspadd                                    -          X         X         X
@@ -2655,7 +2653,7 @@
         use_backend     static   if  url_css url_img extension_img
         default_backend dynamic
 
-  See also : "use_backend", "reqsetbe", "reqisetbe"
+  See also : "use_backend"
 
 
 description <string>