`Spec::Support::Helpers::KeyGeneratorHelper` was added in
857d0391 to generate RSA public key
in openssh format.
At that time we didn't have a gem in Gemfile to do so.

Later, we added `sshkey` gem that allows generating public keys.

Also, we used to have `SSHKeygen` class to generate RSA public keys
in openssh format for specs:

In https://gitlab.com/gitlab-org/gitlab/-/merge_requests/77424,
https://gitlab.com/gitlab-org/gitlab/-/merge_requests/78532
we started using `ssh_data` gem instead of `net-ssh`, `sshkey`,
`net-ssh`, `ed25519`, `bcrypt_pbkdf`, and `SSHKeygen`-class.

We can remove `Spec::Support::Helpers::KeyGeneratorHelper`
in favor of `ssh_data` gem too.