Remove ...LOADED_DEPRECATED and its friends

Use ExtensionRegistryObserver instead of NOTIFICATION_EXTENSION_LOADED_DEPRECATED
from ExtensionTestNotificationObserver.
Also, Remove ExtensionTestNotificationObserver::WaitForExtensionLoad()
since it has a possibility to catch unexpected extension's loaded
notification. Instead of that, use TestExtensionRegistryObserver.

BUG=411568
TEST=browser_tests

Review-Url: https://codereview.chromium.org/2753513006
Cr-Commit-Position: refs/heads/master@{#464703}

• chrome/browser/chromeos/first_run/drive_first_run_browsertest.cc[diff]
• chrome/browser/chromeos/policy/device_cloud_policy_browsertest.cc[diff]
• chrome/browser/extensions/chrome_extension_test_notification_observer.cc[diff]
• chrome/browser/extensions/chrome_extension_test_notification_observer.h[diff]
• chrome/browser/extensions/extension_browsertest.h[diff]
• chrome/browser/extensions/extension_crash_recovery_browsertest.cc[diff]
• extensions/test/extension_test_notification_observer.cc[diff]
• extensions/test/extension_test_notification_observer.h[diff]