Remove non-existent animation variant references

Fixes #8676

binaries/data/mods/public/simulation/templates/units/pers/champion_infantry.xml

@@ -46,7 +46,6 @@
     <Immortal_archer>
       <Entity>units/pers/champion_infantry_archer_upgrade</Entity>
       <Tooltip>Switch to using the bow and arrow.</Tooltip>
-      <Variant>upgrading</Variant>
       <Time>4</Time>
     </Immortal_archer>
   </Upgrade>

binaries/data/mods/public/simulation/templates/units/pers/champion_infantry_archer_upgrade.xml

@@ -44,7 +44,6 @@
     <Immortal_spearman>
       <Entity>units/pers/champion_infantry</Entity>
       <Tooltip>Switch to using a spear and shield.</Tooltip>
-      <Variant>upgrading</Variant>
       <Time>4</Time>
     </Immortal_spearman>
   </Upgrade>

binaries/data/mods/public/simulation/templates/units/rome/infantry_spearman_e.xml

@@ -11,7 +11,6 @@
         <food>100</food>
         <metal>50</metal>
       </Cost>
-      <Variant>upgrading</Variant>
       <Time>8</Time>
     </Centurion>
   </Upgrade>

binaries/data/mods/public/simulation/templates/units/rome/infantry_swordsman_e.xml

@@ -11,7 +11,6 @@
         <food>100</food>
         <metal>50</metal>
       </Cost>
-      <Variant>upgrading</Variant>
       <Time>12</Time>
     </Centurion>
   </Upgrade>