This patch deletes various related files (actors, meshes, textures) that are unused and unlikely to be ever used, since more advanced assets have been added.
* art/actors/structures/:
* `destruct_3x3.xml` is the same as `destruct_wood_3x3.xml`.
* `fndn_1x1.xml` is unused and appears to be an old version; `fndn_1x1pal.xml` is used and visually consistent with the other `fndn_*` actors; the former is therefore replaced with the latter.
* `plot.xml` is unused and useless due to the `fndn_*` actors.
* art/actors/props/structures/construction/: nine unused scaffolds that are visually of a different (and inferior) style to those that are used.
* delete textures only used by these actors
* delete meshes only used by these actors
* delete `wrld_bld_f*.dae` meshes that weren't used anyway
* rename `wrld_settlement_he_a.dae` to `hele_settlement.dae`