Fix unused variable warning in pqMultiBlockInspectorPanel

This fixes an unused variable warning by removing the unused
variable in pqMultiBlockInspectorPanel.

Change-Id: Ie5a920a36ccf4f91826c39c81455874dab1abe41
Merge topic 'multi-block-color-support' into next

056d629 Fix unused variable warning in pqMultiBlockInspectorPanel