removes the duplicate sum of lfs objects

According to the relevant issue lfs objects are being counted twice

What is the current bug behavior?

We add up repository_size + build_artifacts_size + lfs_objects_size + lfs_objects_size

What is the expected correct behavior?

Enforce on: repository_size + lfs_objects_size

This is exactly what the method total_repository_size_does Extracted from the actual code

# models/project_statistics.rb

def total_repository_size
  repository_size + lfs_objects_size
end

What are the relevant issue numbers?

Closes #2055 (closed)