Clean up unused param in RegistryOverrideManager

This param has been unused since http://crrev.com/234367 and makes the method confusing.

BUG=314800

Review URL: https://codereview.chromium.org/575253002

Cr-Commit-Position: refs/heads/master@{#295400}

• base/test/test_reg_util_win.cc[diff]
• base/test/test_reg_util_win.h[diff]
• base/test/test_reg_util_win_unittest.cc[diff]
• chrome/browser/chrome_elf_init_unittest_win.cc[diff]
• chrome/browser/extensions/api/messaging/native_messaging_test_util.cc[diff]
• chrome/browser/media_galleries/media_galleries_test_util.cc[diff]
• chrome/browser/safe_browsing/incident_reporting/environment_data_collection_win_unittest.cc[diff]
• chrome/installer/gcapi/gcapi_last_run_test.cc[diff]
• chrome/installer/gcapi/gcapi_test_registry_overrider.cc[diff]
• chrome/installer/setup/setup_util_unittest.cc[diff]
• chrome/installer/util/google_update_settings_unittest.cc[diff]
• chrome/installer/util/install_util_unittest.cc[diff]
• chrome/installer/util/installer_state_unittest.cc[diff]
• chrome/installer/util/product_state_unittest.cc[diff]
• chrome/installer/util/product_unittest.cc[diff]
• chrome/installer/util/work_item_list_unittest.cc[diff]
• chrome_elf/blacklist/test/blacklist_test.cc[diff]
• chrome_elf/chrome_elf_util_unittest.cc[diff]
• rlz/test/rlz_test_helpers.cc[diff]