Fix pull request pipeline definition for buildkite (#17552)

When the fedramp high feature branch was merged into 8.x the PR pipeline
accidentally duplicated the top level `steps` key. This was a mistake and is
causing issues generating exhaustive test pipeline definition. This commit fixes
the bug by ensuring there is a single `steps` key that defines all the steps in
the pipeline.

Author: donoghuc

.buildkite/pull_request_pipeline.yml

@@ -19,7 +19,6 @@ steps:
       export GRADLE_OPTS="-Xmx2g -Dorg.gradle.daemon=false -Dorg.gradle.logging.level=info"
       ci/license_check.sh -m 4G
 
-steps:
   - label: ":passport_control: License check - Fedramp High Mode"
     key: "license-check-fedramp-high"
     agents: