Fix channel-adapter.adoc for incorrect code block

Author: artembilan

src/reference/asciidoc/channel-adapter.adoc

@@ -53,7 +53,6 @@ public class SourceService {
     }
 }
 ----
-====
 [source, kotlin, role="secondary"]
 .Kotlin DSL
 ----
@@ -64,8 +63,6 @@ fun messageSourceFlow() =
         ...
     }
 ----
-====
-----
 [source, xml, role="secondary"]
 .XML
 ----
@@ -157,7 +154,6 @@ public class MyPojo {
 
 }
 ----
-====
 [source, kotlin, role="secondary"]
 .Kotlin DSL
 ----
@@ -167,8 +163,6 @@ fun outboundChannelAdapterFlow(myPojo: MyPojo) =
         handle(myPojo, "handle")
     }
 ----
-====
-----
 [source, xml, role="secondary"]
 .XML
 ----