Fix autoinstaller failing on autoinstall_everything

Fix autoinstaller failing on autoinstall_everything
https://bugs.webkit.org/show_bug.cgi?id=174830

Patch by Matthew Stewart <matthew_r_stewart@apple.com> on 2017-07-25
Reviewed by Joseph Pecoraro.

* Scripts/webkitpy/thirdparty/__init__.py:
(AutoinstallImportHook.find_module):
(AutoinstallImportHook.install_chromedriver):
(AutoinstallImportHook.install_geckodriver):
(AutoinstallImportHook._install_chromedriver): Deleted.
(AutoinstallImportHook._install_geckodriver): Deleted.

git-svn-id: https://svn.webkit.org/repository/webkit/trunk@219882 268f45cc-cd09-0410-ab3c-d52691b4dbfc