database user: Remove unneeded GET request post-create.

[andrewsomething]

We have reports that the post-create GET requests can unexpectedly fail with a 404 at times despite the create succeeding. For the most part, this request is unnecessary. The information is returned in the POST response. This sets state with that information and removes the unnecessary GET.

=== RUN   TestAccDigitalOceanDatabaseUser_importBasic
=== PAUSE TestAccDigitalOceanDatabaseUser_importBasic
=== RUN   TestAccDigitalOceanDatabaseUser_Basic
=== PAUSE TestAccDigitalOceanDatabaseUser_Basic
=== RUN   TestAccDigitalOceanDatabaseUser_MongoDB
=== PAUSE TestAccDigitalOceanDatabaseUser_MongoDB
=== RUN   TestAccDigitalOceanDatabaseUser_MongoDBMultiUser
=== PAUSE TestAccDigitalOceanDatabaseUser_MongoDBMultiUser
=== RUN   TestAccDigitalOceanDatabaseUser_MySQLAuth
=== PAUSE TestAccDigitalOceanDatabaseUser_MySQLAuth
=== CONT  TestAccDigitalOceanDatabaseUser_importBasic
=== CONT  TestAccDigitalOceanDatabaseUser_MongoDBMultiUser
--- PASS: TestAccDigitalOceanDatabaseUser_importBasic (241.60s)
=== CONT  TestAccDigitalOceanDatabaseUser_MySQLAuth
--- PASS: TestAccDigitalOceanDatabaseUser_MongoDBMultiUser (515.28s)
=== CONT  TestAccDigitalOceanDatabaseUser_MongoDB
--- PASS: TestAccDigitalOceanDatabaseUser_MySQLAuth (286.26s)
=== CONT  TestAccDigitalOceanDatabaseUser_Basic
--- PASS: TestAccDigitalOceanDatabaseUser_Basic (245.87s)
--- PASS: TestAccDigitalOceanDatabaseUser_MongoDB (458.85s)
PASS
ok      github.com/digitalocean/terraform-provider-digitalocean/digitalocean/database   974.256s

[danaelhe]

👍