Remove deprecated resources

Heidi Berryrequested to merge
remove-old-misc-resources into main

This merge request removes deprecated GitLab Terraform resources and updates examples to use their newer replacements. The changes remove documentation for three deprecated resources (gitlab_deploy_token, gitlab_label, gitlab_project_mirror, and gitlab_runner) that will be removed in version 19.0, and updates example code to use the newer gitlab_project_label resource instead of the old gitlab_label resource. This is essentially a cleanup effort to prepare for the next major version by removing outdated functionality and ensuring examples use current best practices.

Part of #6512

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