posts: use storage manager to backup files.

* Perform backups synchronously inside `distribute_files` instead of
  asynchronously in `queue_backup`. Asynchronous backups assumed that
  files are stored on the local filesystem, which isn't true in general.

* Remove obsolete backup service classes.

app/logical/backup_service.rb

@@ -1,9 +0,0 @@
-class BackupService
-  def backup(file_path, options = {})
-    raise NotImplementedError.new("#{self.class}.backup not implemented")
-  end
-
-  def delete(file_path, options = {})
-    raise NotImplementedError.new("#{self.class}.delete not implemented")
-  end
-end

app/logical/null_backup_service.rb

@@ -1,9 +0,0 @@
-class NullBackupService
-  def backup(file_path, options = {})
-    # do nothing
-  end
-
-  def delete(file_path, options = {})
-    # do nothing
-  end
-end

app/logical/s3_backup_service.rb

@@ -1,52 +0,0 @@
-class S3BackupService < BackupService
-  attr_reader :client, :bucket
-
-  def initialize(client: nil, bucket: Danbooru.config.aws_s3_bucket_name)
-    @credentials = Aws::Credentials.new(Danbooru.config.aws_access_key_id, Danbooru.config.aws_secret_access_key)
-    @client = client || Aws::S3::Client.new(credentials: @credentials, region: "us-east-1", logger: Logger.new(STDOUT))
-    @bucket = bucket
-  end
-
-  def backup(file_path, type: nil, **options)
-    keys = s3_keys(file_path, type)
-    keys.each do |key|
-      upload_to_s3(key, file_path)
-    end
-  end
-
-  def delete(file_path, type: nil)
-    keys = s3_keys(file_path, type)
-    keys.each do |key|
-      delete_from_s3(key)
-    end
-  end
-
-protected
-  def s3_keys(file_path, type)
-    name = File.basename(file_path)
-
-    case type
-    when :original
-      [name]
-    when :preview
-      ["preview/#{name}"]
-    when :large
-      ["sample/#{name}"]
-    else
-      raise ArgumentError.new("Unknown type: #{type}")
-    end
-  end
-
-  def delete_from_s3(key)
-    client.delete_object(bucket: bucket, key: key)
-  rescue Aws::S3::Errors::NoSuchKey
-    # ignore
-  end
-
-  def upload_to_s3(key, file_path)
-    File.open(file_path, "rb") do |body|
-      base64_md5 = Digest::MD5.base64digest(File.read(file_path))
-      client.put_object(acl: "public-read", bucket: bucket, key: key, body: body, content_md5: base64_md5)
-    end
-  end
-end