Remove ref name in PR commits page (#25876)

The branch name display here is based on the repo's default branch which
is not correct.

![image](d899f6dc-b240-41ea-9a3e-ea0e103874ad)

For example, if I changed the default branch, the branch name here will
also be changed:

![image](032ead94-2287-4158-a9e4-02e9fb74777d)

![image](e1e6cbbc-31f8-40a2-b99a-508b5b2b3145)
you can confirm this in :
https://try.gitea.io/yp05327/testrepo/pulls/1/commits

I think we do not need to display branch name here, as we already have
the branch info above.

![image](66f30a0c-3c2b-4d26-936d-bbe289f33be0)

routers/web/repo/commit.go

@@ -81,7 +81,6 @@ func Commits(ctx *context.Context) {
 	ctx.Data["Username"] = ctx.Repo.Owner.Name
 	ctx.Data["Reponame"] = ctx.Repo.Repository.Name
 	ctx.Data["CommitCount"] = commitsCount
-	ctx.Data["RefName"] = ctx.Repo.RefName
 
 	pager := context.NewPagination(int(commitsCount), pageSize, page, 5)
 	pager.SetDefaultParams(ctx)
@@ -157,7 +156,7 @@ func Graph(ctx *context.Context) {
 	ctx.Data["Username"] = ctx.Repo.Owner.Name
 	ctx.Data["Reponame"] = ctx.Repo.Repository.Name
 	ctx.Data["CommitCount"] = commitsCount
-	ctx.Data["RefName"] = ctx.Repo.RefName
+
 	paginator := context.NewPagination(int(graphCommitsCount), setting.UI.GraphMaxCommitNum, page, 5)
 	paginator.AddParam(ctx, "mode", "Mode")
 	paginator.AddParam(ctx, "hide-pr-refs", "HidePRRefs")
@@ -203,7 +202,6 @@ func SearchCommits(ctx *context.Context) {
 	}
 	ctx.Data["Username"] = ctx.Repo.Owner.Name
 	ctx.Data["Reponame"] = ctx.Repo.Repository.Name
-	ctx.Data["RefName"] = ctx.Repo.RefName
 	ctx.HTML(http.StatusOK, tplCommits)
 }
 
@@ -247,7 +245,6 @@ func FileHistory(ctx *context.Context) {
 	ctx.Data["Reponame"] = ctx.Repo.Repository.Name
 	ctx.Data["FileName"] = fileName
 	ctx.Data["CommitCount"] = commitsCount
-	ctx.Data["RefName"] = ctx.Repo.RefName
 
 	pager := context.NewPagination(int(commitsCount), setting.Git.CommitsRangeSize, page, 5)
 	pager.SetDefaultParams(ctx)