Update existing prefs for ESR78

A few of our existing prefs have been removed or renamed.

Remove:

• browser.cache.frecency_experiment (removed in https://bugzilla.mozilla.org/show_bug.cgi?id=1573887)
• browser.casting.enabled (removed in https://bugzilla.mozilla.org/show_bug.cgi?id=1393582)
• device.camera.enabled (removed in https://bugzilla.mozilla.org/show_bug.cgi?id=1408957)
• general.useragent.updates.enabled (removed in https://bugzilla.mozilla.org/show_bug.cgi?id=1513574)
• general.useragent.updates.url (removed in https://bugzilla.mozilla.org/show_bug.cgi?id=1513574)
• services.blocklist.update_enabled (removed in https://bugzilla.mozilla.org/show_bug.cgi?id=1458917)
• experiments.enabled (removed in https://bugzilla.mozilla.org/show_bug.cgi?id=1420908)
• browser.syncPromoViewsLeftMap (removed in https://bugzilla.mozilla.org/show_bug.cgi?id=1279224)

Rename:

• geo.wifi.uri --> geo.provider.network.url (renamed in https://bugzilla.mozilla.org/show_bug.cgi?id=1613627)