Creates a _TargetColumn for linear regression. (deprecated)
THIS FUNCTION IS DEPRECATED. It will be removed after 2016-11-12. Instructions for updating: This file will be removed after the deprecation date.Please switch to third_party/tensorflow/contrib/learn/python/learn/estimators/head.py
label_name: String, name of the key in label dict. Can be null if label is a tensor (single headed models).
weight_column_name: A string defining feature column name representing weights. It is used to down weight or boost examples during training. It will be multiplied by the loss of the example.
label_dimension: dimension of the target for multilabels.
An instance of _TargetColumn