Cleaned up Repository#initialize

The "default_branch" argument is never used and the "project" argument
isn't optional.

app/models/project.rb

@@ -342,7 +342,7 @@ class Project < ActiveRecord::Base
   end
   def repository
-    @repository ||= Repository.new(path_with_namespace, nil, self)
+    @repository ||= Repository.new(path_with_namespace, self)
   end
   def commit(id = 'HEAD')

app/models/project_wiki.rb

@@ -123,7 +123,7 @@ class ProjectWiki
   end
   def repository
-    Repository.new(path_with_namespace, default_branch, @project)
+    Repository.new(path_with_namespace, @project)
   end
   def default_branch

app/models/repository.rb

@@ -15,7 +15,7 @@ class Repository
     Gitlab::Popen.popen(%W(find #{repository_downloads_path} -not -path #{repository_downloads_path} -mmin +120 -delete))
   end
-  def initialize(path_with_namespace, default_branch = nil, project = nil)
+  def initialize(path_with_namespace, project)
     @path_with_namespace = path_with_namespace
     @project = project
   end