Bump terraform-root-modules to 0.43.0 (#48)

This is quite a jump but needed for some recent fixes to do with `users`
and `iam`.

One of the changes to how IAM user accounts are managed is to have all IAM users centrally managed in `conf/users`.

vadzim + aliaksandr are not currently working on CP projects so those
users are removed and the other users are in the correct admin groups
across all accounts thanks to the `admin_groups` local, where all admin
groups across enabled accounts are read from SSM.

 are added to these groups as they are included in `admin_groups

conf/iam/terraform.tfvars

@@ -1,40 +1 @@
 accounts_enabled = ["dev", "staging", "prod", "testing", "audit"]
-
-prod_account_user_names = [
-  "admin@cloudposse.co",
-  "erik@cloudposse.com",
-  "vadzim@cloudposse.com",
-  "aliaksandr@cloudposse.com",
-]
-
-staging_account_user_names = [
-  "admin@cloudposse.co",
-  "erik@cloudposse.com",
-  "vadzim@cloudposse.com",
-  "aliaksandr@cloudposse.com",
-]
-
-audit_account_user_names = [
-  "admin@cloudposse.co",
-  "erik@cloudposse.com",
-  "vadzim@cloudposse.com",
-  "aliaksandr@cloudposse.com",
-]
-
-dev_account_user_names = [
-  "admin@cloudposse.co",
-  "erik@cloudposse.com",
-  "vadzim@cloudposse.com",
-  "aliaksandr@cloudposse.com",
-  "solairerove",
-  "josh"
-]
-
-testing_account_user_names = [
-  "admin@cloudposse.co",
-  "erik@cloudposse.com",
-  "vadzim@cloudposse.com",
-  "aliaksandr@cloudposse.com",
-  "josh",
-  "solairerove"
-]

conf/users/terraform.tfvars

@@ -3,7 +3,7 @@ terragrunt = {
     path = "${find_in_parent_folders()}"
   }
   terraform {
-    source = "git::https://github.com/cloudposse/terraform-root-modules.git//aws/users?ref=0.6.0"
+    source = "git::https://github.com/cloudposse/terraform-root-modules.git//aws/users?ref=0.43.0"
     extra_arguments "smtp" {
       commands = ["plan", "apply", "destroy"]
       env_vars = {