refactor: cleanup DefaultAvatar

[satish-ravi]

Description

Replace DefaultAvatar directly with User icon to avoid nested svgs with viewbox.

Test plan

No visual changes in the tx feed

Related issues

N/A

Backwards compatibility

Yes

Network scalability

N/A

[codecov]

Codecov Report

All modified and coverable lines are covered by tests ✅

Project coverage is 88.92%. Comparing base (87e9599) to head (82e78c2).
Report is 1 commits behind head on main.

Additional details and impacted files

@@            Coverage Diff             @@
##             main    #6211      +/-   ##
==========================================
- Coverage   88.93%   88.92%   -0.01%     
==========================================
  Files         737      736       -1     
  Lines       31379    31370       -9     
  Branches     5804     5496     -308     
==========================================
- Hits        27907    27897      -10     
- Misses       3274     3429     +155     
+ Partials      198       44     -154     

Files with missing lines	Coverage Δ
src/components/ContactCircle.tsx	100.00% <100.00%> (ø)

... and 66 files with indirect coverage changes

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[MuckT]

LGTM. Tested locally by navigating to a transaction to check the display of src/components/ContactCircle.tsx