Revert "[lldb-dap] Add missing key for capabilities event. (llvm#142751)"

This reverts commit 159de36.

Author: JDevlieghere

lldb/tools/lldb-dap/EventHelper.cpp

@@ -46,9 +46,7 @@ void SendTargetBasedCapabilities(DAP &dap) {
 
   protocol::Event event;
   event.event = "capabilities";
-  event.body = llvm::json::Object{
-      {"capabilities",
-       llvm::json::Object{{"supportsStepInTargetsRequest", false}}}};
+  event.body = llvm::json::Object{{"supportsStepInTargetsRequest", false}};
   dap.Send(event);
 }
 // "ProcessEvent": {