Remove duplicate definition of UNUSED(V)

[nitaicaro]

Already defined in https://github.com/nitaicaro/valkey/blob/2977a790d77c861df24dbe917e858c90824d3c10/src/dict.c#L56

[codecov]

Codecov Report

All modified and coverable lines are covered by tests ✅

Project coverage is 70.25%. Comparing base (f2bbd1f) to head (366c5c4).

Additional details and impacted files

@@             Coverage Diff              @@
##           unstable     #755      +/-   ##
============================================
- Coverage     70.30%   70.25%   -0.05%     
============================================
  Files           111      111              
  Lines         60300    60300              
============================================
- Hits          42393    42366      -27     
- Misses        17907    17934      +27     

Files	Coverage Δ
src/dict.c	97.53% <ø> (ø)

... and 12 files with indirect coverage changes