This reverts commit 55e2b43.

This reverts commit 55e2b43.

BUILD_ROOT was being set to ${CI_PROJECT_DIR} but this causes issues
when passed as a component input because CI_PROJECT_DIR doesn't exist
when inputs are resolved. The variable is not actually needed since
CI jobs run in the project directory by default.

Projects can define BUILD_ROOT locally if their build scripts need it,
but it shouldn't be passed to components as an input.

🤖 Generated with [Claude Code](https://claude.com/claude-code)

Co-Authored-By: Claude <[email protected]>

Update docs/sphinx/dev_guide/ci.rst to reflect the migration from
template-based CI to GitLab CI Components:

- Updated .gitlab-ci.yml description to mention it now uses GitLab CI
  Components (requires GitLab 17.0+)
- Replaced references to subscribed-pipelines.yml and
  custom-jobs-and-variables.yml with the new split files:
  - custom-jobs.yml - Job templates for child pipelines
  - custom-variables.yml - Machine-specific allocation variables
- Clarified that these files are created and customized by each project
  based on templates from RADIUSS Shared CI
- Updated pipeline launching section to explain component syntax and
  list available components (base-pipeline, utility-draft-pr-filter,
  machine-specific pipelines)
- Explained that machine pipelines are now defined inline in
  .gitlab-ci.yml using trigger syntax with component includes

…tion

Update docs/sphinx/dev_guide/ci_tasks.rst to reflect the migration from
template-based CI to GitLab CI Components:

- Updated run parameters section to reference custom-variables.yml and
  custom-jobs.yml instead of the old custom-jobs-and-variables.yml file
- Clarified that these files are created and customized by each project
  for its specific needs
- Updated RAJAPerf CI section to reflect the new file structure and
  mention that it uses GitLab CI Components from radiuss-shared-ci
- Removed references to subscribed-pipelines.yml which no longer exists

…variables.yml