Update bitFlyer promo image in onboarding flow (Sept 2021)

[Miyayes]

Description

Replace bitFlyer images in onboarding with the following asset.

• The image should link out to: https://twitter.com/bravesoftwarejp
• Use the image asset below:

@soi-tnk

[stephendonner]

Verified PASSED using

Brave	1.30.80 Chromium: 94.0.4606.50 (Official Build) beta (x86_64)
Revision	0c1ac2c4842a4746c27c937c1a0453f98da1a972-refs/branch-heads/4606@{#1049}
OS	macOS Version 11.6 (Build 20G165)

Steps:

1. Clean profile
2. Set OS region to Japan
3. Enabled Rewards
4. Verified that the new bitFlyer image appears at end of onboarding flow
5. Verified that clicking new bitFlyer image opened a new page to https://twitter.com/bravesoftwarejp

example	example