front: hide provisional curve in the speed space chart

[SarahBellaha]

Closes #7967

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Codecov Report

Attention: Patch coverage is 0% with 1 line in your changes missing coverage. Please review.

Project coverage is 28.25%. Comparing base (c390cb4) to head (aa57860).

Files	Patch %	Lines
...tionResult/components/SpeedSpaceChart/d3Helpers.ts	0.00%	1 Missing ⚠️

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Additional details and impacted files

@@             Coverage Diff              @@
##                dev    #7992      +/-   ##
============================================
- Coverage     28.25%   28.25%   -0.01%     
  Complexity     2075     2075              
============================================
  Files          1276     1276              
  Lines        156197   156187      -10     
  Branches       3084     3084              
============================================
- Hits          44140    44126      -14     
- Misses       110216   110220       +4     
  Partials       1841     1841              

Flag	Coverage Δ
core	75.03% <ø> (ø)
editoast	70.98% <ø> (-0.05%)	⬇️
front	9.92% <0.00%> (+<0.01%)	⬆️
gateway	2.34% <ø> (ø)
railjson_generator	87.49% <ø> (ø)
tests	72.93% <ø> (ø)

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[SharglutDev]

Lgtm and tested, thank you for the fix !