Remove Griffin flag for Brave Talk

[bsclifton]

Test plan

1. Remove BraveTalk study for the channel in question (staging)
2. Launch Brave (fresh profile) pointing at staging (I think you can use --variations-server-url=https://variations.bravesoftware.com/seed)
3. You should see the Brave Talk promo (bottom right)
4. If you click Edit Cards you should be able to add Brave Talk

Description

Brave Talk has a card available on New Tab Page and also a promo flyout that shows. This was put behind a flag with brave/brave-core#9605

We can remove this config now that it's live. After that is done and fix makes its way to release channel, we can remove study (tracked with brave/brave-variations#133)

[stephendonner]

@bsclifton @rebron @kjozwiak are we going to uplift this into 1.31.x, or will it ride the trains to 1.32.x? I verified it on brave/brave-core#10311 (comment).

[kjozwiak]

A bit late seeing this but at this point, leaving it in 1.32.x and letting it ride the trains sounds like a good idea considering we're releasing 1.31.x on Tuesday and planning on creating the final RC either tonight/Sunday early afternoon.

[stephendonner]

Verified PASSED using

Brave	1.32.74 Chromium: 95.0.4638.54 (Official Build) dev (x86_64)
Revision	d31a821ec901f68d0d34ccdbaea45b4c86ce543e-refs/branch-heads/4638@{#871}
OS	macOS Version 11.6 (Build 20G165)

Steps:

1. new profile
2. launched Brave using --enable-logging=stderr --vmodule="*/variations/*"=6,"*/bat-native-ledger/*"=6,"*/brave_rewards/*"=6,"*/bat-native-ads/*"=6,"*/bat-native-confirmations/*"=6,"*/brave_ads/*"=9,"*/brave_user_model/*"=6 --brave-ads-staging --brave-ads-debug --rewards=staging=true,reconcile-interval=3 --variations-server-url=https://variations.bravesoftware.com/seed
3. opened a new-tab page
4. confirmed and tested the Brave Talk video-camera icon launches https://talk.brave.com/widget
5. confirmed Brave Talk's widget shows up in Edit Cards -> Cards -> + Add
6. confirmed clicking on + Add adds Brave Talk to the the active widgets on the NTP
7. confirmed clicking on Start video call takes the user to https://talk.brave.com/widget
8. confirmed About your data link goes to https://brave.com/privacy/browser/#brave-talk-learn
9. confirmed that traveling to the future, 3 days from now, the Brave Talk promo "tooltip" popup shows up

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