Improve TribeExecution deleteAllStructures 🏛️ (#3777)

## Description:

`deleteAllStructures` did not check for `isMarkedForDeletion`, not very
clean. Now its clean.
Also rename to `deleteNextStructure` because its not possible to delete
more than 1 structure at a time.

## Please complete the following:

- [X] I have added screenshots for all UI updates
- [X] I process any text displayed to the user through translateText()
and I've added it to the en.json file
- [X] I have added relevant tests to the test directory
- [X] I confirm I have thoroughly tested these changes and take full
responsibility for any bugs introduced

## Please put your Discord username so you can be contacted if a bug or
regression is found:

FloPinguin

src/core/execution/TribeExecution.ts

@@ -60,7 +60,7 @@ export class TribeExecution implements Execution {
     }
 
     this.acceptAllAllianceRequests();
-    this.deleteAllStructures();
+    this.deleteNextStructure();
     this.maybeAttack();
   }
 
@@ -83,11 +83,13 @@ export class TribeExecution implements Execution {
     }
   }
 
-  private deleteAllStructures() {
+  private deleteNextStructure() {
+    if (!this.tribe.canDeleteUnit()) return;
     for (const unit of this.tribe.units()) {
-      if (Structures.has(unit.type()) && this.tribe.canDeleteUnit()) {
-        this.mg.addExecution(new DeleteUnitExecution(this.tribe, unit.id()));
-      }
+      if (!Structures.has(unit.type())) continue;
+      if (unit.isMarkedForDeletion()) continue;
+      this.mg.addExecution(new DeleteUnitExecution(this.tribe, unit.id()));
+      return;
     }
   }