resolve naming conflict on case insensitive FS

[karlbenedict]

This file is not used (based on a grep -R Sorting_Example.png * search within the repository root). When pulling the repo into a case insensitive file system the following error is generated.

warning: the following paths have collided (e.g. case-sensitive paths
on a case-insensitive filesystem) and only one from the same
colliding group is in the working tree:

'fig/Sorting_Example.png'
'fig/sorting_example.png'

As this file is not currently used in the files in the repo it seems safe to remove it and eliminate the pull error.

[hoytpr]

Hi @karlbenedict and I confirmed the pull error so thanks very much for catching this.