models/user: Remove unused sync find() fn

[Turbo87]

Everything is using the async variant now, so lets get rid of the sync one 🎉

[codecov]

Codecov Report

Attention: Patch coverage is 71.42857% with 2 lines in your changes missing coverage. Please review.

Project coverage is 89.22%. Comparing base (2c10682) to head (005f1d6).
Report is 7 commits behind head on main.

Files with missing lines	Patch %	Lines
src/auth.rs	50.00%	1 Missing ⚠️
src/bin/crates-admin/verify_token.rs	0.00%	1 Missing ⚠️

Additional details and impacted files

@@           Coverage Diff           @@
##             main    #9983   +/-   ##
=======================================
  Coverage   89.21%   89.22%           
=======================================
  Files         292      292           
  Lines       30387    30384    -3     
=======================================
  Hits        27109    27109           
+ Misses       3278     3275    -3     

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