fix: Fix creating roles with name prefix AND inline policy

[aleskiontherun]

Description

Fixes creating roles with name prefix AND inline policy.

Motivation and Context

name_prefix attribute in inline policy resource contained var.role_name, which could be null when var.role_name_prefix is used instead. It is also not possible to set both var.role_name and var.role_name_prefix, which causes an error for aws_iam_role resource. Having var.role_name in inline policy's name_prefix is redundant because it is part of the role itself and can't be used outside of the role's context, so it is safe to remove.

There is actually an example in https://github.com/terraform-aws-modules/terraform-aws-iam/blob/e13cb1e5d1356ccb2ddd1bae0ad4c3a17e88eee2/examples/iam-assumable-role/main.tf with both role_name_prefix and inline_policy_statements vars set, which fails for me with The expression result is null. Cannot include a null value in a string template. error, not sure why it wasn't detected earlier, I guess it might depend on Terraform version.

Breaking Changes

None

How Has This Been Tested?

• I have updated at least one of the examples/* to demonstrate and validate my change(s)
• I have tested and validated these changes using one or more of the provided examples/* projects

• I have executed pre-commit run -a on my pull request