chore: removes extensionOnly from the web3onboard example

[christopherferreira9]

Explanation

This PR removes extensionOnly option from the SDK options since it is redundant.

References

Checklist

• I've updated the test suite for new or updated code as appropriate
• I've updated documentation (JSDoc, Markdown, etc.) for new or updated code as appropriate
• I've highlighted breaking changes using the "BREAKING" category above as appropriate

[codecov]

Codecov Report

All modified and coverable lines are covered by tests ✅

Project coverage is 74.14%. Comparing base (8ab1cf1) to head (43ccc34).

Additional details and impacted files

@@            Coverage Diff             @@
##             main    #1149      +/-   ##
==========================================
- Coverage   74.26%   74.14%   -0.12%     
==========================================
  Files         181      181              
  Lines        4297     4297              
  Branches     1052     1052              
==========================================
- Hits         3191     3186       -5     
- Misses       1106     1111       +5     

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