purge TCF agent cra^Wstuff

it's dead code

src/plugins/debugger/debuggerconstants.h

@@ -100,7 +100,6 @@ enum DebuggerStartMode
     StartExternal,         // Start binary found in file system
     AttachExternal,        // Attach to running process by process id
     AttachCrashedExternal, // Attach to crashed process by process id
-    AttachTcf,             // Attach to a running Target Communication Framework agent
     AttachCore,            // Attach to a core file
     StartRemote            // Start and attach to a remote process
 };