Remove elastictranscoder client following the service deprecation

Author: kdaily

.changes/next-release/api-change-elastictranscoder-50945.json

@@ -0,0 +1,5 @@
+{
+  "type": "api-change",
+  "category": "``elastictranscoder``",
+  "description": "The elastictranscoder client has been removed following the deprecation of the service."
+}