Outlier detection and removal using scatter-plots and histograms
Yes. This code does nothing but to plot the points for two chosen columns and assign different color and markers to them. It does not do any outlier selection/removal. 
Column 3 and 4 (which are features in your dataset) are reasonably predictive of different classes.
Plot a histogram. See if there is any clear disjoint in among the bars. Investigate a little time to find a suitable bin size.


In addition, the title of your question does not match the content. Can you please update the question?