Remove unused 'reference_point' from MultiObjectiveBenchmarkProblem

[esantorella]

Summary: As title

Differential Revision: D47383874

[facebook-github-bot]

This pull request was exported from Phabricator. Differential Revision: D47383874

[codecov-commenter]

Codecov Report

Patch coverage has no change and project coverage change: -0.01 :warning:

Comparison is base (f738de3) 95.04% compared to head (148f826) 95.04%.

:exclamation: Current head 148f826 differs from pull request most recent head 4ec3e01. Consider uploading reports for the commit 4ec3e01 to get more accurate results

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Additional details and impacted files

@@            Coverage Diff             @@
##             main    #1713      +/-   ##
==========================================
- Coverage   95.04%   95.04%   -0.01%     
==========================================
  Files         452      452              
  Lines       41805    41802       -3     
==========================================
- Hits        39734    39731       -3     
  Misses       2071     2071              

Impacted Files	Coverage Δ
ax/benchmark/benchmark_problem.py	100.00% <ø> (ø)
ax/benchmark/tests/test_benchmark_problem.py	100.00% <ø> (ø)

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