Merge pull request cms-sw#34064 from bsunanda/Run3-gex76

Run3-gex76 Remove one unused material for ZDC definition

Author: cmsbuild

Geometry/ForwardCommonData/data/zdcmaterials/2021/v1/zdcmaterials.xml

@@ -1,7 +1,6 @@
 <?xml version="1.0"?>
 <DDDefinition>
  <MaterialSection label="zdcmaterials.xml">
-  <ElementaryMaterial name="Galactic" density="1e-22*mg/cm3" symbol=" " atomicWeight="1.01*g/mole" atomicNumber="1"/>
   <CompositeMaterial name="Luminosity Gas" density="6.5933*mg/cm3" symbol=" " method="mixture by weight">
    <MaterialFraction fraction="0.01">
     <rMaterial name="materials:Nitrogen"/>