Remove support for legacy WebKit Notifications
Remove support for legacy WebKit Notifications

All the instances of ENABLE_LEGACY_NOTIFICATIONS has been removed.

BUG=348019

Review URL: https://codereview.chromium.org/192703004

git-svn-id: bf5cd6ccde378db821296732a091cfbcf5285fbd@168875 bbb929c8-8fbe-4397-9dbb-9b2b20218538

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