delete testbed plugins (#69661)

* delete testbed plugins

* remove FTR tests based on KP testbed

Author: pgayvallet

src/dev/build/tasks/copy_source_task.js

@@ -34,9 +34,7 @@ export const CopySourceTask = {
         '!src/test_utils/**',
         '!src/fixtures/**',
         '!src/legacy/core_plugins/tests_bundle/**',
-        '!src/legacy/core_plugins/testbed/**',
         '!src/legacy/core_plugins/console/public/tests/**',
-        '!src/plugins/testbed/**',
         '!src/cli/cluster/**',
         '!src/cli/repl/**',
         '!src/es_archiver/**',