Follow-up from workflow rules variables

When implementing (!52085 (merged)) "Support variables for workflow rules" (#294232 (closed)), we decided to keep variables and yaml_variables in order to avoid massive change that may end up a bug.

In this issue, we will remove those.

With:

• Remove: TODO link: variables: root_and_job_variables (lib/gitlab/ci/config/entry/processable.rb)
• Remove: TODO link: variables: variables (lib/gitlab/ci/config/normalizer/matrix_strategy.rb)
• Remove: TODO link: yaml_variables: transform_to_yaml_variables(job[:variables]) (lib/gitlab/ci/yaml_processor/result.rb)
• Remove: TODO link: yaml_variables: yaml_variables (lib/gitlab/web_ide/config/entry/terminal.rb)
• Change this usage: https://gitlab.com/gitlab-org/gitlab/-/blob/33686d0429e51117a9b63613b8ca5074b23dd1cc/app/services/security/ci_configuration/sast_parser_service.rb#L108-125
• Remove inherit? logic from Config::Entry::Inherit::Variables
• Remove :yaml_variables from workflow_attributes of Result (!52085 (comment 530226685))
  • !52085 (comment 530226697)
• Refactor root_variables_inheritance || true

Maybe...

We should convert job_variables to yaml_variables and use a single term for it...