Hide QR code in Rewards Settings (uplift to 1.18.x)

[brave-builds]

Uplift of #7350
Fixes brave/brave-browser#13053

Approved, please ensure that before merging:

• You have checked CI and the builds, lint, and tests all pass or are not related to your PR.
• You have tested your change on Nightly.
• The PR milestones match the branch they are landing to.

After you merge:

• The associated issue milestone is set to the smallest version that the changes is landed on.

[kjozwiak]

test-browser failed on macOS due to RewardsBrowserTest.UpholdLimitNoBAT and RewardsPromotionBrowserTest.ClaimViaPanel failing as per https://ci.brave.com/job/pr-brave-browser-pr7350_bsc-remove-qr-code_1.18.x-macos/1/execution/node/250/log/. However, these are known intermittent issues and are being tracked via brave/brave-browser#12704 and brave/brave-browser#12605.

00:07:47  2 tests failed:
00:07:47      RewardsBrowserTest.UpholdLimitNoBAT (../../brave/components/brave_rewards/browser/test/rewards_browsertest.cc:397)
00:07:47      RewardsPromotionBrowserTest.ClaimViaPanel (../../brave/components/brave_rewards/browser/test/rewards_promotion_browsertest.cc:201)

[kjozwiak]

Uplift into 1.18.x approved after deliberating with @brave/uplift-approvers. QA has verified the PR on Nightly as per #7350 (comment).