This patch cleans up some `template_structure*` lines.
Split off from D2855:
* Defines attack sounds only in those structure templates that define an <Attack>.
Split off from D2993:
* Defines <BuildingAI> only in those structure templates that define an <Attack>. Split off from D3000:
* Removes <Sound> from `template_structure_special.xml`, since most of its children have different values.
* Removes <TerritoryInfluence> from `template_structure_special.xml`, since most of its children have different values.
* Purges unused <BuildRestrictions/Category> lines.