Issue7 add ds user delete

Fixes #7 

Adds cURL call to `mb-user-api` which removes user entries that have mixed case email addresses.

Related:
https://github.com/DoSomething/mb-users-api/issues/60
This is minor, but you do `getenv('DS_USER_API_HOST') . ':' . getenv('DS_USER_API_PORT')` a couple lines above too. Maybe just do it once with like a ...

`$baseUrl = getenv('DS_USER_API_HOST') . ':' . getenv('DS_USER_API_PORT')`

And then here you'd have:

`$deleteUserApiUrl = $baseUrl . '/user ...etc...'`