Remove unused strings from en.json (#2582)

## Description:

This PR removes several unused strings from en.json.
Leaving unused entries increases Crowdin storage usage and makes
translation management harder, so they should be cleaned up regularly.

The removed strings were originally added in the following PRs but are
not used anywhere in the codebase:
- #2146
- #2060
- #2233

## 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:

aotumuri

resources/lang/en.json

@@ -146,7 +146,6 @@
     "compact_map": "Compact Map",
     "max_timer": "Game length (minutes)",
     "disable_nukes": "Disable Nukes",
-    "automatic_difficulty": "Automatic Difficulty",
     "enables_title": "Enable Settings",
     "start": "Start Game"
   },
@@ -272,7 +271,6 @@
     "infinite_troops": "Infinite troops",
     "donate_troops": "Donate troops",
     "compact_map": "Compact Map",
-    "automatic_difficulty": "Automatic Difficulty",
     "enables_title": "Enable Settings",
     "player": "Player",
     "players": "Players",
@@ -650,7 +648,6 @@
     "flag": "Flag",
     "chat": "Chat",
     "target": "Target",
-    "break": "Break",
     "break_alliance": "Break Alliance",
     "alliance": "Alliance",
     "send_alliance": "Send Alliance",
@@ -662,10 +659,7 @@
     "title_with_name": "Send Troops to {name}",
     "available_tooltip": "Your current available troops",
     "min_keep": "Min keep",
-    "min_keep_pct": "(30%)",
     "slider_tooltip": "{{percent}}% • {{amount}}",
-    "toggle_attack_bar_mode": "Use attack bar to send troops",
-    "warning_attackbar": "Once enabled, you can't open this modal directly. You'll only send troops via the attack bar.",
     "aria_slider": "Troops slider",
     "capacity_note": "Receiver can accept only {{amount}} right now."
   },