Remove Fedora 34 platform definition from puppet-agent repository

Process

The work here consists of two steps that should be done in separate commits. The first step is to remove the platform from ext/build_defaults.yaml.

The second step is to remove the platform.rb file in configs/platforms, and any special casing required for that specific platform. The latter may include, but is not limited to, any platform-specific files in the resources directory (e.g., patches, scripts), specific casing in the .rb files found in the configs/components and configs/projects directories, and special casing in the acceptance tests found in the acceptance directory.

The agent repo has multiple maintenance branches as well as a master branch. If you are unsure about what branch to target your PR at, feel free to ping the Puppet Romania team on the prod-puppet-agent channel. Note that you only need to make a PR to the lowest agent maintenance branch, since there is some merge-up automation already in place for the agent repo that will ensure your work gets merged-up to the later branches. Also make sure that the Puppet Romania team members review your PR.

Context

Removing the platform from ext/build_defaults.yaml in the first step ensures that we do not ship the built agent to our nightly repositories. The second step completely removes the platform and all mentions of it from the agent repository so that we cannot even build the agent; this is a more radical change. The main reason we create two commits here instead of one is due to an (unlikely) scenario where we want to stop shipping the platform but still test it out in CI (i.e., do only the first step).