Delete empty GraphTest.php
Delete empty GraphTest.php

Initially created as a stub in
Iad816d3a88f4417731b36330250e03066a04205d, but never
actually used.

Change-Id: I9bc808a4595146835a41c2fc7e525e6e9060dd38

wikimedia/mediawiki-extensions-Graph,wikimedia/mediawiki-extensions-Graph