FastTree regression samples use FastForest instead

[najeeb-kazmi]

I noticed some FastTree samples using FastForest, namely:

machinelearning/docs/samples/Microsoft.ML.Samples/Dynamic/Trainers/Regression/FastTree.cs

Lines 30 to 32 in fa62c81

	var pipeline = mlContext.Regression.Trainers.FastForest(
	labelColumnName: nameof(DataPoint.Label),
	featureColumnName: nameof(DataPoint.Features));

and

machinelearning/docs/samples/Microsoft.ML.Samples/Dynamic/Trainers/Regression/FastTreeTweedie.cs

Lines 30 to 32 in fa62c81

	var pipeline = mlContext.Regression.Trainers.FastForest(
	labelColumnName: nameof(DataPoint.Label),
	featureColumnName: nameof(DataPoint.Features));

Appears to be a mistake introduced in PR #3948.