remove baffling 0.25px letter-spacing with system font

src/alf/fonts.ts

···
     if (IS_WEB) {
       style.fontFamily = style.fontFamily || WEB_FONT_FAMILIES
     }
-
-    /**
-     * Overridden to previous spacing for the `system` font option.
-     * https://github.com/bluesky-social/social-app/commit/2419096e2409008b7d71fd6b8f8d0dd5b016e267
-     */
-    style.letterSpacing = 0.25
   }
 }