Backport of 'Remove package OS check from deployer task' - 18.10

What does this MR do and why?

Backport of Remove package OS check from deployer task to 18-10-stable. Removes the unnecessary OS version check from the gitlab_com:deployer rake task, which does not work (no package is attached to the job) and is irrelevant since the deployer pipeline only uses DEPLOY_VERSION, DEPLOY_USER, and DEPLOY_ENVIRONMENT.

MR acceptance checklist

This checklist encourages us to confirm any changes have been analyzed to reduce risks in quality, performance, reliability, security, and maintainability.

• This MR is backporting a bug fix, documentation update, or spec fix, previously merged in the default branch.
• The original MR has been deployed to GitLab.com (not applicable for documentation or spec changes).
• This MR has a severity label assigned (if applicable).

Note to the merge request author and maintainer

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