awx Do not add env vars if they do not add content

SUMMARY

This cleans up the job_env of a job.

"job_env": {
        "JOB_ID": "25",
        "AWX_HOST": "https://platformhost/",
        "INVENTORY_ID": "3",
        "MAX_EVENT_RES": "700000",
        "PROJECT_REVISION": "347e44fea036c94d5f60e544de006453ee5c71ad",
        "RUNNER_OMIT_EVENTS": "False",
        "ANSIBLE_FORCE_COLOR": "True",
        "AWX_PRIVATE_DATA_DIR": "/tmp/awx_25_4v0h263v",
        "ANSIBLE_UNSAFE_WRITES": "1",
        "AWX_ISOLATED_DATA_DIR": "/runner/artifacts/25",
        "ANSIBLE_STDOUT_CALLBACK": "awx_display",
        "ANSIBLE_CALLBACK_PLUGINS": "/runner/artifacts/25/callback",
        "ANSIBLE_HOST_KEY_CHECKING": "False",
        "RUNNER_ONLY_FAILED_EVENTS": "False",
        "ANSIBLE_RETRY_FILES_ENABLED": "False",
        "ANSIBLE_SSH_CONTROL_PATH_DIR": "/runner/cp",
        "ANSIBLE_INVENTORY_UNPARSED_FAILED": "True",
        "ANSIBLE_PARAMIKO_RECORD_HOST_KEYS": "False"
    },

No longer will we set the ANSIBLE_ROLES_PATH and others every time. They should only get set if the actually downloaded some collections or roles from the user requirements.yml. Since build_env runs after the project update run, this should be valid, but this still needs verification that it doesn't break playbooks with this content.