[KGA-106] [KGA-79] [KGA-89] dev: remove useless computation in uint256_fast_exp"

[enitrat]

https://github.com/code-423n4/2024-09-kakarot-findings/issues/2

removes a useless line that compute uint256_fast_exp one too many times.

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This change is 

[notion-workspace]

Opcode EXP for large even number can make starknet transaction revert due to running out of steps

[codecov]

Codecov Report

All modified and coverable lines are covered by tests ✅

Project coverage is 63.6%. Comparing base (474951c) to head (c98794a).
Report is 1 commits behind head on main.

Additional details and impacted files

@@           Coverage Diff           @@
##            main   #1603     +/-   ##
=======================================
- Coverage   63.6%   63.6%   -0.1%     
=======================================
  Files         44      44             
  Lines       8332    8331      -1     
=======================================
- Hits        5301    5299      -2     
- Misses      3031    3032      +1     

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[notion-workspace]

EXP can make VM run out of resources

[notion-workspace]

Exponential Redundant Calculations in uint256_fast_exp used for EXP opcode