chore: remove legacy GitHub Actions role

[glitchedmob]

Removes the shared GitHub Actions role now that all four consumers use repository-scoped roles.

• Delete the legacy role and its state, SSM, SES, and application IAM inline policies
• Remove the obsolete shared role ARN output
• Preserve the GitHub OIDC provider, application SES sender policies, and repository-scoped roles
• Produce a plan of 0 additions, 0 changes, and 5 deletions