ARROW-2962: [Packaging] Bintray descriptor files are no longer needed

Wait for [build-302](https://github.com/kszucs/crossbow/branches/all?utf8=%E2%9C%93&query=build-302) to pass

Author: Krisztián Szűcs <szucs.krisztian@gmail.com>

Closes #2357 from kszucs/ARROW-2962 and squashes the following commits:

7445b8c <Krisztián Szűcs> remove bintray descriptors
8baabda <Krisztián Szűcs> don't update descriptor in rake task

dev/tasks/linux-packages/package-task.rb

@@ -266,7 +266,6 @@ def define_version_task
       task :update do
         update_debian_changelog
         update_spec
-        update_descriptor
       end
     end
   end
@@ -325,13 +324,4 @@ def update_spec
     end
   end
 
-  def update_descriptor
-    Dir.glob("**/descriptor.json") do |descriptor_json|
-      update_content(descriptor_json) do |content|
-        content = content.sub(/"name": "\d+\.\d+\.\d+.*?"/) do
-          "\"name\": \"#{@version}\""
-        end
-      end
-    end
-  end
 end