Remove playground blueprint

web/app/playground/__init__.py

-from flask import Blueprint
-
-
-playground = Blueprint('playground', __name__)
-from . import events, views  # noqa

web/app/playground/views.py

-from flask import render_template
-from flask_login import login_required
-from . import playground
-
-
-@playground.route('/')
-@login_required
-def index():
-    return render_template('playground/index.html.j2',
-                           title='Playground')