Bug 1709647 - Remove unused NS_CHANGE_COLOR_IF_SAME_AS_BG. r=jfkthame

It was introduced in bug 1024930, but it is unused since.

Differential Revision: https://phabricator.services.mozilla.com/D114389

layout/generic/nsTextFrame.cpp

@@ -4148,16 +4148,6 @@ bool nsTextPaintStyle::InitSelectionColorsAndShadow() {
                     &nsStyleText::mWebkitTextFillColor);
       mSelectionTextColor =
           EnsureDifferentColors(frameColor, mSelectionBGColor);
-    } else if (mSelectionTextColor == NS_CHANGE_COLOR_IF_SAME_AS_BG) {
-      nscolor frameColor =
-          SVGUtils::IsInSVGTextSubtree(mFrame)
-              ? mFrame->GetVisitedDependentColor(&nsStyleSVG::mFill)
-              : mFrame->GetVisitedDependentColor(
-                    &nsStyleText::mWebkitTextFillColor);
-      if (frameColor == mSelectionBGColor) {
-        mSelectionTextColor = LookAndFeel::Color(
-            LookAndFeel::ColorID::TextSelectForegroundCustom, mFrame);
-      }
     } else {
       EnsureSufficientContrast(&mSelectionTextColor, &mSelectionBGColor);
     }

servo/components/style/values/specified/color.rs

@@ -174,8 +174,6 @@ pub enum SystemColor {
     #[css(skip)]
     TextSelectForeground,
     #[css(skip)]
-    TextSelectForegroundCustom,
-    #[css(skip)]
     TextSelectBackgroundDisabled,
     #[css(skip)]
     TextSelectBackgroundAttention,

widget/LookAndFeel.h

@@ -564,12 +564,6 @@ class LookAndFeel {
 // Of course if other plaforms work like the Mac, they can use it too.
 #define NS_DONT_CHANGE_COLOR NS_RGB(0x01, 0x01, 0x01)
 
-// Similar with NS_DONT_CHANGE_COLOR, except NS_DONT_CHANGE_COLOR would returns
-// complementary color if fg color is same as bg color.
-// NS_CHANGE_COLOR_IF_SAME_AS_BG would returns
-// ColorID::TextSelectForegroundCustom if fg and bg color are the same.
-#define NS_CHANGE_COLOR_IF_SAME_AS_BG NS_RGB(0x02, 0x02, 0x02)
-
 // ---------------------------------------------------------------------
 //  Special colors for ColorID::IME* and ColorID::SpellCheckerUnderline
 // ---------------------------------------------------------------------

widget/nsXPLookAndFeel.cpp

@@ -206,7 +206,6 @@ static const char sColorPrefs[][41] = {
     "ui.textForeground",
     "ui.textSelectBackground",
     "ui.textSelectForeground",
-    "ui.textSelectForegroundCustom",
     "ui.textSelectBackgroundDisabled",
     "ui.textSelectBackgroundAttention",
     "ui.textHighlightBackground",