build: remove dead headlines

Author: jippi

README.md

@@ -37,14 +37,6 @@
     - [`label.skip_if` (optional)](#labelskip_if-optional)
 - [Expr-lang information](#expr-lang-information)
   - [Attributes](#attributes)
-    - [project](#project)
-    - [project.labels](#projectlabels)
-    - [group](#group)
-    - [merge_request](#merge_request)
-    - [merge_request.diff_stats](#merge_requestdiff_stats)
-    - [merge_request.first_commit](#merge_requestfirst_commit)
-    - [merge_request.last_commit](#merge_requestlast_commit)
-    - [merge_request.labels](#merge_requestlabels)
   - [Functions](#functions)
     - [`merge_request.modified_files`](#merge_requestmodified_files)
     - [`duration`](#duration)