remove deprecated option from alacritty config

.config/alacritty/alacritty.yml

@@ -22,6 +22,8 @@ window.dimensions:
   columns: 80
   lines: 24
 
+window.opacity: 1.0
+
 # Adds this many blank pixels of padding around the window
 # Units are physical pixels; this is not DPI aware.
 # (change requires restart)
@@ -86,11 +88,6 @@ font:
     x: 0
     y: 0
 
-  # OS X only: use thin stroke font rendering. Thin strokes are suitable
-  # for retina displays, but for non-retina you probably want this set to
-  # false.
-  use_thin_strokes: true
-
 cursor:
   style: Beam
 
@@ -164,9 +161,6 @@ bell:
   animation: EaseOutExpo
   duration: 0
 
-# Background opacity
-background_opacity: 1.0
-
 # Mouse bindings
 #
 # Currently doesn't support modifiers. Both the `mouse` and `action` fields must