Update Startpage icons

[bsclifton]

Fixes brave/brave-browser#15515

Submitter Checklist:

• I confirm that no security/privacy review is needed, or that I have requested one
• There is a ticket for my issue
• Used Github auto-closing keywords in the PR description above
• Wrote a good PR/commit description
• Added appropriate labels (QA/Yes or QA/No; release-notes/include or release-notes/exclude; OS/...) to the associated issue
• Checked the PR locally: npm run test -- brave_browser_tests, npm run test -- brave_unit_tests, npm run lint, npm run gn_check, npm run tslint
• Ran git rebase master (if needed)

Reviewer Checklist:

• A security review is not needed, or a link to one is included in the PR description
• New files have MPL-2.0 license header
• Adequate test coverage exists to prevent regressions
• Major classes, functions and non-trivial code blocks are well-commented
• Changes in component dependencies are properly reflected in gn
• Code follows the style guide
• Test plan is specified in PR before merging

After-merge Checklist:

• The associated issue milestone is set to the smallest version that the
  changes has landed on
• All relevant documentation has been updated, for instance:
  • https://github.com/brave/brave-browser/wiki/Deviations-from-Chromium-(features-we-disable-or-remove)
  • https://github.com/brave/brave-browser/wiki/Proxy-redirected-URLs
  • https://github.com/brave/brave-browser/wiki/Fingerprinting-Protections
  • https://github.com/brave/brave-browser/wiki/Brave%E2%80%99s-Use-of-Referral-Codes
  • https://github.com/brave/brave-browser/wiki/Custom-Headers
  • https://github.com/brave/brave-browser/wiki/Web-Compatibility-Exceptions-in-Brave
  • https://github.com/brave/brave-browser/wiki/QA-Guide
  • https://github.com/brave/brave-browser/wiki/P3A

Test Plan:

1. Android fresh install
2. Go through Onboarding
3. Verify new icon is used during onboarding (for Startpage)

[deeppandya]

LGTM

[deeppandya]

@bsclifton @jamesmudgett at some point, we should think about changing all search engine icons to vector drawable of possible. I can create a separate issue to track the change.

[bsclifton]

@deeppandya sure, that would be great 😄

[deeppandya]

Created an issue brave/brave-browser#15517

[bsclifton]

Merging as errors are unrelated; this is just modifying an existing image (no tests around this)

[bsclifton]

Whoops; turns out I had added an image (unintentionally) which broke things on Android build. Should have looked a bit closer at CI ☹️ If this PR is uplifted, please be sure to also uplift #8656

[bsclifton]

Follow up - icons in this PR were too large; fixed with #8701 (so if this is uplifted, that would be needed too)

[srirambv]

Verification passed on OnePlus 6T with Android 10 running 1.26.11 x64 Nightly build

• Verified StartPage icon is similar to the other ones during onboarding