Update twisted version in webkitpy.thirdparty.autoinstalled module.

Update twisted version in webkitpy.thirdparty.autoinstalled module.
https://bugs.webkit.org/show_bug.cgi?id=154667

Reviewed by Ryosuke Niwa.

Use twisted_15_5_0 for the twisted module used by run-benchmark because there is a bug in twisted 12.1.0 which sometimes stops the test.
Installing twisted was introduced in https://bugs.webkit.org/show_bug.cgi?id=147082 for run-benchmark script.
Since buildbot relies on twisted 12.1.0 and has not been verified the compatibility on twisted 15.5.0, it would be more secure to use an individual version for run-benchmark script.

* Scripts/webkitpy/benchmark_runner/http_server_driver/http_server/twisted_http_server.py:
* Scripts/webkitpy/thirdparty/__init__.py:
(AutoinstallImportHook.find_module):
(AutoinstallImportHook._install_twisted_15_5_0):
(AutoinstallImportHook._install_twisted): Deleted.

git-svn-id: http://svn.webkit.org/repository/webkit/trunk@208205 268f45cc-cd09-0410-ab3c-d52691b4dbfc