Fix a transient failure in mini_pipeline_graph_spec

This spec failed reliably with a specific run order (see issue), the
reasons for which are still unknown. This simplification resolves the
failure.

Closes https://gitlab.com/gitlab-org/gitlab-ce/issues/34323

spec/features/projects/commit/mini_pipeline_graph_spec.rb

 require 'rails_helper'
 feature 'Mini Pipeline Graph in Commit View', :js do
-  let(:user) { create(:user) }
   let(:project) { create(:project, :public, :repository) }
-  before do
-    sign_in(user)
-  end
-
   context 'when commit has pipelines' do
     let(:pipeline) do
       create(:ci_empty_pipeline,
@@ -15,21 +10,14 @@ feature 'Mini Pipeline Graph in Commit View', :js do
               ref: project.default_branch,
               sha: project.commit.sha)
     end
-    let(:build) do
-      create(:ci_build, pipeline: pipeline)
-    end
-
-    before do
+    let(:build) { create(:ci_build, pipeline: pipeline) }
+    it 'displays a mini pipeline graph' do
       build.run
       visit project_commit_path(project, project.commit.id)
-    end
-    it 'should display a mini pipeline graph' do
       expect(page).to have_selector('.mr-widget-pipeline-graph')
-    end
-    it 'should show the builds list when stage is clicked' do
       first('.mini-pipeline-graph-dropdown-toggle').click
       wait_for_requests
@@ -38,6 +26,8 @@ feature 'Mini Pipeline Graph in Commit View', :js do
         expect(page).to have_selector('.ci-status-icon-running')
         expect(page).to have_content(build.stage)
       end
+
+      build.drop
     end
   end