Allow dismissing the privacy mode notification

The privacy mode notification was not able to be dismissed from the
popup UI. It should have been dismissed after clicking "Learn more",
but that button opens a new tab first before dismissing the flag.
Opening the new tab kills the pop UI process before it has a chance
to set that flag, so it never gets set.

Re-ordering the handler to set the flag first avoids this problem.

ui/app/pages/home/home.component.js

@@ -99,8 +99,8 @@ export default class Home extends PureComponent {
                         descriptionText={t('privacyModeDefault')}
                         acceptText={t('learnMore')}
                         onAccept={() => {
-                          window.open('https://medium.com/metamask/42549d4870fa', '_blank', 'noopener')
                           unsetMigratedPrivacyMode()
+                          window.open('https://medium.com/metamask/42549d4870fa', '_blank', 'noopener')
                         }}
                         key="home-privacyModeDefault"
                       />,