fix donation not set on singleplayer (#2093)

## Description:
Bug: Donation to nations was not allowed in single player mode.

Always allow donation to Nations. Simplify the donation check logic.

## 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:

evan

resources/lang/en.json

@@ -130,9 +130,7 @@
     "disable_nations": "Disable Nations",
     "instant_build": "Instant build",
     "infinite_gold": "Infinite gold",
-    "donate_gold": "Donate gold",
     "infinite_troops": "Infinite troops",
-    "donate_troops": "Donate troops",
     "disable_nukes": "Disable Nukes",
     "enables_title": "Enable Settings",
     "start": "Start Game"