Skip initialization of referral system for the default referral code

[bsclifton]

Test plan

See brave/brave-core#8103

Background

Originally added in brave/brave-core#1982 (to address #2547), Brave will default to promo code BRV001.

We have since sunset the referral program (see https://brave.com/referral-program-update/) except for a few specific cases. For more information on how the referral program works please see https://github.com/brave/brave-browser/wiki/Brave%E2%80%99s-Use-of-Referral-Codes

Description

We should skip initialization of the referral system for the default code (BRV001)

[kjozwiak]

As per conversation with @BrendanEich @bsclifton and others, we'll want to get this into 1.21.x. Adding release/blocking.

[srirambv]

Verification passed on OnePlus 6T with Android 10 running 1.21.73 x64 build

• Verified able to see the referral id under nonua on 1.20.108 build
  
• Verified /promo/initialize/nonua wasn't called on startup when running 1.21.73
  
• Verified brave://local-state contains BRV001 for referral code even when /promo/initialize/nonua is removed
  
• Verified download_id is not present in brave://local-state via the referral header
  

[GeetaSarvadnya]

Verification passed on

Brave | 1.21.73 Chromium: 89.0.4389.72 (Official Build) (64-bit)
-- | --
Revision | 3f345f156bfd157bd1bea06310e55f3fb2490359-refs/branch-heads/4389@{#1393}
OS | Windows 10 OS Version 2004 (Build 19041.804)

• Verified using Charles Proxy that I can no longer see the referral_code: BRV001 section in a JSON blob under initalize, nonua, as I can, with release build 1.20.110, for the host https://laptop-updates.brave.com/.
• Verified that the BRV001 referral was being used in brave://local-state

1.20.110	1.21.73	Referral/promo code via brave://local-state 1.21.73

---

Verification passed on

Brave	1.21.73 Chromium: 89.0.4389.72 (Official Build) (64-bit)
Revision	3f345f156bfd157bd1bea06310e55f3fb2490359-refs/branch-heads/4389@{#1393}
OS	Ubuntu 18.04 LTS

Verified test plan from brave/brave-core#8103 (comment)

---

Verified passed with

Verified test plan from brave/brave-core#8103 (comment)

• ensured that /promo/initialize/nonua wasn't being called at startup as per the examples below
• ensured that the BRV001 referral was being used in brave://local-state

Before (1.21.71)	After (1.21.73)	Referral code via brave://local-state (1.21.73)