Removed double consideration of same timestamp

[Oribow]

When searching for an acceptable timestamp dictionary t-CURRENT_RESPONSE_TIME_PERCENTILE_WINDOW is considered twice, because t-CURRENT_RESPONSE_TIME_PERCENTILE_WINDOW-0 == t-CURRENT_RESPONSE_TIME_PERCENTILE_WINDOW+0

[codecov]

Codecov Report

Merging #1332 into master will decrease coverage by 0.21%.
The diff coverage is 100.00%.

@@            Coverage Diff             @@
##           master    #1332      +/-   ##
==========================================
- Coverage   81.29%   81.07%   -0.22%     
==========================================
  Files          24       24              
  Lines        2208     2209       +1     
  Branches      333      333              
==========================================
- Hits         1795     1791       -4     
- Misses        329      332       +3     
- Partials       84       86       +2     

Impacted Files	Coverage Δ
locust/stats.py	88.76% <100.00%> (+0.02%)	⬆️
locust/clients.py	91.66% <0.00%> (-5.21%)	⬇️

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[heyman]

Thanks!