Worker AI for mods, step 2 (#5998)

* Worker AI for mods, step 2

Support for removing terrain features, both when we need to get rid of them for a resource, and when they plain reduce the yield of a tile

Note that the "Remove <improvement>" was implemented WAY before templating and uniques were a thing - the correct solution in these enlightened times would be to separate the improvement *name* from the *effect*, so we could have e.g. a "Deforestation" improvement which would contain botth ["Removes [Jungle]", "Removes [Forest]"] or whatnot.

For now I Constant'D the "Remove " so we can at least follow where it's used.

* Reverted some of the auto-formatting so the PR is cleaner

* Caught 'nullify yields' unique for terrain removal

core/src/com/unciv/Constants.kt

@@ -63,6 +63,7 @@ object Constants {
 
     const val rising = "Rising"
     const val lowering = "Lowering"
+    const val remove = "Remove "
     
     const val minimumMovementEpsilon = 0.05
 }