DOC: Rethink recommending eval/query in "Enhancing performance" section of user guide
#### Location of the documentation

https://pandas.pydata.org/pandas-docs/stable/user_guide/enhancingperf.html#expression-evaluation-via-eval

#### Documentation problem

It seems that `eval` and `query` are not faster than boolean indexing in latest versions of Pandas. See [here](https://stackoverflow.com/questions/49936557/pandas-dataframe-loc-vs-query-performance) for example and [my own experience](https://groups.google.com/forum/#!topic/pydata/Bwj5Vd00yiI) is the same.

#### Suggested fix for documentation

Remove this section from "Ehnancing perfromance".