Revert "Disable voting for mwext-ImageMetrics-qunit"

ImageMetrics depends on EventLogging which has been added to the Jenkins
jobs with https://gerrit.wikimedia.org/r/#/c/165456/

A manual test confirmed the qunit job now pass.

This reverts commit fe5ce90314bb65246470aea95410ce5d5694246d.

Bug: 71782
Change-Id: I5e823d902a4656239b7f41ff02f57c3f9846dab7