Update i18n

Author: florianduros

src/i18n/strings/en_EN.json

@@ -2426,13 +2426,10 @@
             "custom_font_name": "System font name",
             "custom_font_size": "Use custom size",
             "custom_theme_add": "Add custom theme",
-            "custom_theme_add_button": "Add theme",
             "custom_theme_downloading": "Downloading custom theme...",
             "custom_theme_error_downloading": "Error downloading theme",
             "custom_theme_help": "Enter the URL of a custom theme you want to apply.",
             "custom_theme_invalid": "Invalid theme schema.",
-            "custom_theme_success": "Theme added!",
-            "custom_theme_url": "Custom theme URL",
             "custom_themes": "Custom themes",
             "dialog_title": "<strong>Settings:</strong> Appearance",
             "font_size": "Font size",
@@ -2443,8 +2440,7 @@
             "layout_bubbles": "Message bubbles",
             "layout_irc": "IRC (Experimental)",
             "match_system_theme": "Match system theme",
-            "timeline_image_size": "Image size in the timeline",
-            "use_high_contrast": "Use high contrast"
+            "timeline_image_size": "Image size in the timeline"
         },
         "automatic_language_detection_syntax_highlight": "Enable automatic language detection for syntax highlighting",
         "autoplay_gifs": "Autoplay GIFs",