Remove superfluous EchoServer class

[perlun]

This was added in 5d97e39, but I think it was an earlier experiment that ever ended up being used (there's a separate EchoService and Client class in the example/ class which was added in that commit). The problem with including this in agent/src/main/java/ is that it gets included in the published .jar file, which is almost certainly unintentional.

[perlun]

Found by coincidence when running unzip -v ~/.attachme/attachme-agent-1.2.4.jar locally. 🙂

$ unzip -v ~/.attachme/attachme-agent-1.2.4.jar 
Archive:  /home/plundberg/.attachme/attachme-agent-1.2.4.jar
 Length   Method    Size  Cmpr    Date    Time   CRC-32   Name
--------  ------  ------- ---- ---------- ----- --------  ----
       0  Defl:N        2   0% 2023-10-20 13:35 00000000  META-INF/
     233  Defl:N      153  34% 2023-10-20 13:35 c1bd5a9c  META-INF/MANIFEST.MF
    3445  Defl:N     1844  47% 2023-10-20 13:35 92e711df  EchoServer.class
       0  Defl:N        2   0% 2023-10-20 13:35 00000000  com/
       0  Defl:N        2   0% 2023-10-20 13:35 00000000  com/attachme/
       0  Defl:N        2   0% 2023-10-20 13:35 00000000  com/attachme/agent/
     811  Defl:N      415  49% 2023-10-20 13:35 8ab3654e  com/attachme/agent/AttachmeServer$Listener$1.class
     201  Defl:N      156  22% 2023-10-20 13:35 54434a28  com/attachme/agent/Agent$1.class
    1739  Defl:N      913  48% 2023-10-20 13:35 ede6b065  com/attachme/agent/AttachmeClient.class
     921  Defl:N      553  40% 2023-10-20 13:35 8330bdf4  com/attachme/agent/PortResolver.class
     571  Defl:N      333  42% 2023-10-20 13:35 ce592d29  com/attachme/agent/AttachmeServer$Listener.class
     819  Defl:N      430  48% 2023-10-20 13:35 b14ac9b3  com/attachme/agent/AttachmeServer$Console$1.class
     510  Defl:N      308  40% 2023-10-20 13:35 a0446f8e  com/attachme/agent/AttachmeServer$Console.class
    4330  Defl:N     2080  52% 2023-10-20 13:35 54128564  com/attachme/agent/Agent.class
    3995  Defl:N     1885  53% 2023-10-20 13:35 ef807f4b  com/attachme/agent/CommandPortResolver.class
    1181  Defl:N      611  48% 2023-10-20 13:35 5f693bc2  com/attachme/agent/UnixHandler.class
    1430  Defl:N      643  55% 2023-10-20 13:35 dfac8068  com/attachme/agent/ProcessRegisterMsg.class
    1206  Defl:N      622  48% 2023-10-20 13:35 f2cbdfac  com/attachme/agent/WindowsHandler.class
    2166  Defl:N      950  56% 2023-10-20 13:35 22336b07  com/attachme/agent/PortCommandHandler.class
    4837  Defl:N     2425  50% 2023-10-20 13:35 1de04361  com/attachme/agent/AttachmeServer.class
    4250  Defl:N     2251  47% 2023-10-20 13:35 b38d700e  com/attachme/agent/Agent$DebugPortTask.class
--------          -------  ---                            -------
   32645            16580  49%                            21 files