Remove redundant methods

Because we can assume that 3rd party plugins that use `detach_process`
or `detach_multi_process` includes `Fluent::DetachProcessMixin` or
`Fluent::DetachMultiProcessMixin`.

lib/fluent/compat/input.rb

@@ -44,16 +44,6 @@ def before_shutdown
       def shutdown
         super
       end
-
-      def detach_process(&block)
-        log.warn "detach_process is not supported in this version. ignored."
-        block.call
-      end
-
-      def detach_multi_process(&block)
-        log.warn "detach_process is not supported in this version. ignored."
-        block.call
-      end
     end
   end
 end

lib/fluent/compat/output.rb

@@ -190,16 +190,6 @@ def start
           end
         end
       end
-
-      def detach_process(&block)
-        log.warn "detach_process is not supported in this version. ignored."
-        block.call
-      end
-
-      def detach_multi_process(&block)
-        log.warn "detach_process is not supported in this version. ignored."
-        block.call
-      end
     end
 
     class MultiOutput < Fluent::Plugin::BareOutput