refactor(git service): fetch last pipeline method can be private

After implementing detached pipelines, this method is only used within
the gitlab_service module.

src/gitlab_service.ts

@@ -202,7 +202,7 @@ export async function getAllGitlabProjects(): Promise<VsProject[]> {
   return Promise.all(projectsWithUri);
 }
 
-export async function fetchLastPipelineForCurrentBranch(
+async function fetchLastPipelineForCurrentBranch(
   workspaceFolder: string,
 ): Promise<RestPipeline | null> {
   const project = await fetchCurrentPipelineProject(workspaceFolder);

src/status_bar.test.js

@@ -113,7 +113,6 @@ describe('status_bar', () => {
       gitLabService.fetchCurrentPipelineProject.mockReturnValue(project);
       // FIXME: why is closing issue fetched from normal remote and pipeline result from pipeline remote?
       gitLabService.fetchCurrentProject.mockReturnValue(project);
-      gitLabService.fetchLastPipelineForCurrentBranch.mockReturnValue(null);
     });
 
     afterEach(() => {
@@ -154,7 +153,6 @@ describe('status_bar', () => {
       gitLabService.fetchCurrentPipelineProject.mockReturnValue(project);
       // FIXME: why is closing issue fetched from normal remote and pipeline result from pipeline remote?
       gitLabService.fetchCurrentProject.mockReturnValue(project);
-      gitLabService.fetchLastPipelineForCurrentBranch.mockReturnValue(null);
     });
 
     afterEach(() => {