Revert "Reserve ecommerce service username on edx-platform."

Bad data migration: assumes the email address being used is unique
This reverts commit 448f4d51.

lms/djangoapps/commerce/migrations/0001_add_ecommerce_service_user.py

-# -*- coding: utf-8 -*-
-from south.utils import datetime_utils as datetime
-from south.db import db
-from south.v2 import DataMigration
-from django.db import models
-
-from django.conf import settings
-from django.contrib.auth.models import User
-
-class Migration(DataMigration):
-
-    def forwards(self, orm):
-        """Add the service user."""
-        user = User.objects.create(username=settings.ECOMMERCE_SERVICE_WORKER_USERNAME)
-        user.set_unusable_password()
-        user.save()
-
-    def backwards(self, orm):
-        """Remove the service user."""
-        User.objects.get(username=settings.ECOMMERCE_SERVICE_WORKER_USERNAME).delete()
-
-    models = {
-        
-    }
-
-    complete_apps = ['commerce']
-    symmetrical = True

lms/envs/common.py

@@ -2577,7 +2577,6 @@ ECOMMERCE_PUBLIC_URL_ROOT = None
 ECOMMERCE_API_URL = None
 ECOMMERCE_API_SIGNING_KEY = None
 ECOMMERCE_API_TIMEOUT = 5
-ECOMMERCE_SERVICE_WORKER_USERNAME = 'ecommerce_worker'
 
 # Reverification checkpoint name pattern
 CHECKPOINT_PATTERN = r'(?P<checkpoint_name>[^/]+)'