Remove 'Structure' preferred class from elephants, shorten max range.

Elephants were designed to prefer targeting structures. This is not
particularly historically accurate, and makes them rather annoying to
use against enemy units, reducing their efficiency.

This simply removes the preferred class, making elephants easier to
handle while keeping their usage as siege units for some civilisations.

Max-range is reduced slightly as the previous one was extremely large
for a melee unit.

Approved by: Nescio, wraitii
Patch by: borg-
Differential Revision: https://code.wildfiregames.com/D2786
This was SVN commit r23752.

binaries/data/mods/public/simulation/templates/template_unit_champion_elephant_melee.xml

@@ -7,10 +7,9 @@
         <Pierce>0</Pierce>
         <Crush>150.0</Crush>
       </Damage>
-      <MaxRange>8.0</MaxRange>
+      <MaxRange>5.0</MaxRange>
       <PrepareTime>750</PrepareTime>
       <RepeatTime>1500</RepeatTime>
-      <PreferredClasses datatype="tokens">Structure</PreferredClasses>
     </Melee>
   </Attack>
   <Identity>

binaries/data/mods/public/simulation/templates/template_unit_hero_elephant_melee.xml

@@ -12,10 +12,9 @@
         <Pierce>0</Pierce>
         <Crush>50.0</Crush>
       </Damage>
-      <MaxRange>8.0</MaxRange>
+      <MaxRange>5.0</MaxRange>
       <PrepareTime>500</PrepareTime>
       <RepeatTime>1000</RepeatTime>
-      <PreferredClasses datatype="tokens">Structure</PreferredClasses>
     </Melee>
   </Attack>
   <Cost>