Deprecate IPocketAccess.getUpgrades

I think this left over from CCTweaks or Peripheral++. It doesn't really
make sense as an API - if/when we add multiple upgrades, we'll want a
different API for this.

projects/common/src/main/java/dan200/computercraft/shared/pocket/core/PocketServerComputer.java

@@ -104,6 +104,7 @@ public class PocketServerComputer extends ServerComputer implements IPocketAcces
     }
 
     @Override
+    @Deprecated(forRemoval = true)
     public Map<ResourceLocation, IPeripheral> getUpgrades() {
         return upgrade == null ? Collections.emptyMap() : Collections.singletonMap(upgrade.getUpgradeID(), getPeripheral(ComputerSide.BACK));
     }