Removed EnterpriseMiddleware

EnterpriseMiddleware set value of user's enterprise customer in session. In order to get value of enterprise customer it calls `enterprise/api/v1/enterprise-learner` API. Sometimes this middleware is called many times which result in many call to the under lying API and throttling of API causes 429 http errors.
We are not removing that middleware and storing value of user's enterprise customer in session inside underlying method.
ENT-1849

Removed pdb statement