Remove the -webkit-fullscreen-volume-* pseudos, they're dead code.

third_party/WebKit/Source/core/css/CSSValueKeywords.json5

 {
   // The mode argument is used to limit the keyword to be used only for certain
   // CSSParserModes. Values that have the prefix -internal- are only allowed by
   // CSSParserModes listed in allowInternalPropertyAndValue()
 
   parameters: {
     mode: {},
   },
 
   //
@@ skipping 630 matching lines @@
     "radio",
     "push-button",
     "square-button",
     "button",
     "button-bevel",
     "inner-spin-button",
     "listbox",
     "listitem",
     "media-enter-fullscreen-button",
     "media-exit-fullscreen-button",
-    "media-fullscreen-volume-slider",
-    "media-fullscreen-volume-slider-thumb",
     "media-mute-button",
     "media-play-button",
     "media-overlay-play-button",
     "media-toggle-closed-captions-button",
     "media-slider",
     "media-sliderthumb",
     "media-volume-slider-container",
     "media-volume-slider",
     "media-volume-sliderthumb",
     "media-controls-background",
@@ skipping 463 matching lines @@
     // shape
     // rect
     // round
 
     // color-gamut
     // srgb
     "p3",
     "rec2020",
   ],
 }