Remove old migration tasks

You should update to 6.0 before proceed with update to higher version.
So its no reason to keep old tasks any more.
It should be still available in 6-0-stable but not in master

lib/tasks/migrate/migrate_global_projects.rake

-desc "GITLAB | Migrate Global Projects to Namespaces"
-task migrate_global_projects: :environment do
-  found = Project.where(namespace_id: nil).count
-  if found > 0
-    puts "Global namespace is deprecated. We found #{found} projects stored in global namespace".yellow
-    puts "You may abort this task and move them to group/user namespaces manually."
-    puts "If you want us to move this projects under owner namespaces then continue"
-    ask_to_continue
-  else
-    puts "No global projects found. Proceed with update.".green
-  end
-
-  Project.where(namespace_id: nil).find_each(batch_size: 20) do |project|
-    begin
-      project.transfer(project.owner.namespace)
-      print '.'
-    rescue => ex
-      puts ex.message
-      print 'F'
-    end
-  end
-end
-

lib/tasks/migrate/migrate_groups.rake

-desc "GITLAB | Migrate Groups to match v6.0"
-task migrate_groups: :environment do
-  puts "This will add group owners to group membership"
-  ask_to_continue
-
-  Group.find_each(batch_size: 20) do |group|
-    begin
-      group.send :add_owner
-      print '.'
-    rescue => ex
-      puts ex.message
-      print 'F'
-    end
-  end
-end
-

lib/tasks/migrate/migrate_inline_notes.rake

-desc "GITLAB | Migrate inline notes"
-task migrate_inline_notes: :environment do
-  Note.where('line_code IS NOT NULL').find_each(batch_size: 100) do |note|
-    begin
-      note.set_diff
-      if note.save
-        print '.'
-      else
-        print 'F'
-      end
-    rescue
-      print 'F'
-    end
-  end
-end
-

lib/tasks/migrate/migrate_keys.rake

-desc "GITLAB | Migrate SSH Keys"
-task migrate_keys: :environment do
-  puts "This will add fingerprint to ssh keys in db"
-  puts "If you have duplicate keys https://github.com/gitlabhq/gitlabhq/issues/4453 all but the first will be deleted".yellow
-  ask_to_continue
-
-  Key.find_each(batch_size: 20) do |key|
-    if key.valid? && key.save
-      print '.'
-    elsif key.fingerprint.present?
-      puts "\nDeleting #{key.inspect}".yellow
-      key.destroy
-    else
-      print 'F'
-    end
-  end
-  print "\n"
-end
-
-

lib/tasks/migrate/migrate_milestones.rake

-desc "GITLAB | Migrate Milestones"
-task migrate_milestones: :environment do
-  Milestone.where(state: nil).update_all(state: 'active')
-end

lib/tasks/migrate/migrate_mr.rake

-# This taks will reload commits/diff for all merge requests
-desc "GITLAB | Migrate Merge Requests"
-task migrate_merge_requests: :environment do
-  puts "Since 5.1 old merge request serialization logic was replaced with a better one."
-  puts "It makes old merge request diff invalid for GitLab 5.1+"
-  puts "* * *"
-  puts "This will rebuild commits/diffs info for existing merge requests."
-  puts "You will lose merge request diff if its already merged."
-  ask_to_continue
-
-  MergeRequest.find_each(batch_size: 20) do |mr|
-    mr.st_commits = []
-    mr.save
-    mr.reload_code
-    print '.'
-  end
-end
-

lib/tasks/migrate/migrate_note_linecode.rake

-desc "GITLAB | Migrate Note LineCode"
-task migrate_note_linecode: :environment do
-  Note.inline.each do |note|
-    index = note.diff_file_index
-    if index =~ /^\d{1,10}$/ # is number. not hash.
-      hash = Digest::SHA1.hexdigest(note.noteable.diffs[index.to_i].new_path)
-      new_line_code = note.line_code.sub(index, hash)
-      note.update_column :line_code, new_line_code
-      print '.'
-    end
-  end
-end
-