[ci] Remove jenkins config (elastic#173745)

We've migrated off and shut down our instance. These files are no longer
needed.

.buildkite/pull_requests.json

@@ -15,17 +15,13 @@
       "build_drafts": false,
       "trigger_comment_regex": "^(?:(?:buildkite\\W+)?(?:build|test)\\W+(?:this|it))|^\\/ci$",
       "always_trigger_comment_regex": "^(?:(?:buildkite\\W+)?(?:build|test)\\W+(?:this|it))|^\\/ci$",
-      "skip_ci_labels": ["skip-ci", "jenkins-ci"],
+      "skip_ci_labels": ["skip-ci"],
       "skip_target_branches": ["6.8", "7.11", "7.12"],
       "enable_skippable_commits": true,
       "skip_ci_on_only_changed": [
         "^dev_docs/",
         "^docs/",
         "^rfcs/",
-        "^.ci/.+\\.yml$",
-        "^.ci/es-snapshots/",
-        "^.ci/pipeline-library/",
-        "^.ci/Jenkinsfile_[^/]+$",
         "^\\.github/",
         "\\.md$",
         "\\.mdx$",
@@ -71,10 +67,6 @@
         "^dev_docs/",
         "^docs/",
         "^rfcs/",
-        "^.ci/.+\\.yml$",
-        "^.ci/es-snapshots/",
-        "^.ci/pipeline-library/",
-        "^.ci/Jenkinsfile_[^/]+$",
         "^\\.github/",
         "\\.md$",
         "\\.mdx$",