Brave News Top Sources Migration fix

[fallaciousreasoning]

The |GetLocales| function was changed to return the V1 locale. Unfortunately this broke the top sources migration, as the V1 locale for most regions is "" (the empty string). This meant when we ran the migration users would be subscribed to the Top Sources channel but only in the "" region. When switching to V2 they would get a proper locale, but they wouldn't be subscribed to sources in that region.

The fix is to only subscribe to Top Sources when the V2 flag is enabled.

[LaurenWags]

@fallaciousreasoning can you please add OS/Desktop or OS/Android - or both, depending on where this fix needs to be QA'ed? Thanks!

cc @rebron @kjozwiak

[fallaciousreasoning]

Done, sorry about that.

[stephendonner]

Verification PASSED using

Brave	1.46.73 Chromium: 107.0.5304.62 (Official Build) beta (x86_64)
Revision	1eec40d3a5764881c92085aaee66d25075c159aa-refs/branch-heads/5304@{#942}
OS	macOS Version 11.7 (Build 20G817)

default, Brave News enabled (no source changes) - PASSED

1. launched Brave
2. opened a new-tab page
3. scrolled down and clicked on Show Brave News
4. restarted Brave
5. set brave://flags/#brave-news-v2 to Enabled
6. opened a new-tab page
7. scrolled and ensured I still saw articles
8. clicked on Customize
9. confirmed I was subscribed to the Top Sources feed

News, v1	brave://flags	News, v2	News, v2

customized Brave News feed (via source list) - FAILED(*)

1. launched Brave
2. opened a new-tab page
3. scrolled down
4. clicked on Show Brave News
5. clicked on Customize
6. removed the following:

• all Crypto sources
• all Fashion sources
• all Sports sources

7. opened brave://flags
8. set brave://flags/#brave-news-v2 to Enabled
9. clicked on Relaunch
10. opened a new-tab page
11. clicked on Customize

v1	v2

Logged:

• Brave News v2 migration follows sources disabled in v1 #26184

customized Brave News feed (via additional RSS feed) - PASSED

1. launched Brave
2. opened a new-tab page
3. scrolled down
4. clicked on Show Brave News
5. clicked on Customize
6. added https://planet.mozilla.org/atom.xml
7. scrolled, and ensured I saw a feed article from Planet Mozilla
8. opened brave://flags
9. set brave://flags/#brave-news-v2 to Enabled
10. clicked on Relaunch
11. opened a new-tab page
12. clicked on Customize
13. ensured I saw Planet Mozilla both in the Following and Discover (search) sections

example	example	example	example

Logged #26184