Algod: Remove unused 404 resp in simulate endpoint

[ahangsu]

Summary

As I was reading #5159, I noticed an addition of 404 response to /v2/transactions/simulate, while handler.go impl does not have notFound return.

So I remove the 404 response, as it is unused here.

[bbroder-algo]

this went away with the decision to remove the feature gate configuration parameter.

[codecov]

Codecov Report

Merging #5211 (f6be04a) into master (942eee1) will decrease coverage by 16.77%.
The diff coverage is n/a.

@@             Coverage Diff             @@
##           master    #5211       +/-   ##
===========================================
- Coverage   52.48%   35.71%   -16.77%     
===========================================
  Files         441      441               
  Lines       55098    55098               
===========================================
- Hits        28917    19679     -9238     
- Misses      23830    33353     +9523     
+ Partials     2351     2066      -285     

see 242 files with indirect coverage changes

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