[ML] The ML plugin doesn't need socket permissions (#65079)

I think these got propagated accidentally when X-Pack
was split into multiple plugins.

Backport of #65067

Author: droberts195

x-pack/plugin/ml/src/main/plugin-metadata/plugin-security.policy

@@ -1,7 +1,4 @@
 grant {
-  // needed for multiple server implementations used in tests
-  permission java.net.SocketPermission "*", "accept,connect";
-
   // needed for Windows named pipes in machine learning
   permission java.io.FilePermission "\\\\.\\pipe\\*", "read,write";
 };