[BUG][crystal][client] .rspec and .rubocop.yml should be removed

Created by: cyangle

Bug Report Checklist

• Have you provided a full/minimal spec to reproduce the issue?
• Have you validated the input using an OpenAPI validator (example)?
• Have you tested with the latest master to confirm the issue still exists?
• Have you searched for related issues/PRs?
• What's the actual output vs expected output?
• [Optional] Sponsorship to speed up the bug fix or feature request (example)

Description

.rspec and .rubocop.yml should be removed as they are ruby gem configuration files

openapi-generator version

All versions supporting crystal client generation. It's not a regression.

OpenAPI declaration file content or url

Generation Details

Issue exists in the generated crystal client pet store sample code

Steps to reproduce

Generate crystal client pet store sample code

Related issues/PRs

Suggest a fix

Remove .rspec and .rubocop.yml templates from crystal client generator