…rn#14771)"

This reverts commit bcaf381.

The test in reverted commit is useless and doesn't rely on the code
implementation. The commit claims to fix scikit-learn#7141, where the isolation forest is
trained on the identical values leading to the degenerated trees.

Under described circumstances, one may check that the exact score value for
every point in the parameter space is zero (or 0.5 depending on if we are
talking about initial paper or scikit-learn implementation).
However, there is no special code in existing implementation, and the score
value is a subject of rounding erros. So, for instance, for 100 identical input
samples, we have a forest predicting everything as inliners, but for 101 input
samples, we have a forest predicting everything as outliers. The decision is
taken only based on floating point rounding error value.

One may check this by changing the number of input samples:

    X = np.ones((100, 10))

to

    X = np.ones((101, 10))

or something else.