Don't show branded wallpaper notification in NTP for Super Referral

[simonhong]

Description

Notification for guiding about how to hide SI is only valid for Sponsored Images.
See https://bravesoftware.slack.com/archives/CT7JC4KBM/p1587357584128900

Test plan

1. Do an install that uses Super Referral (put promoCode file in directory for TECHNIK; see Implement NTP Custom homepage ("super referral") brave-core#4866 for more steps)
2. Launch into brave
3. Enable rewards
4. Pull up new tab until it shows super referral page
5. Verify the rewards widget on NTP does NOT look like this:
   

[kjozwiak]

Verification PASSED on macOS 10.15.4 x64 using the following build:

Brave | 1.8.85 Chromium: 81.0.4044.122 (Official Build) (64-bit)
-- | --
Revision | 44f4233f08910d83b146130c1938256a2e05b136-refs/branch-heads/4044@{#963}
OS | macOS Version 10.15.4 (Build 19E287)

Went through the STR outlined under #9329 and ensured that the You're getting paid to view this background image message wasn't being displayed in the Rewards modal under the NTP:

Also ensured that the You're getting paid to view this background image was still being displayed when a user enabled Rewards that's going through the normal NTP SI flow:

Verification passed on

Brave	1.8.85 Chromium: 81.0.4044.122 (Official Build) (64-bit)
Revision	44f4233f08910d83b146130c1938256a2e05b136-refs/branch-heads/4044@{#963}
OS	Windows 10 OS Version 1803 (Build 17134.1006)

Went through the STR outlined under #9329 and ensured that the You're getting paid to view this background image message wasn't being displayed in the Rewards modal under the NTP:

[btlechowski]

Setting as OS/Windows and OS/macOS because referrals are unavailable on Linux