Remove LinkSystemColors and NewSystemColors feature flags

Both LinkSystemColors and NewSystemColors have been stable for
several months. Removing the flags as a result.
http://crrev.com/c/1829645

Bug: 1015968
Change-Id: I8e4926941c634349ff47c0c9dd86ae4d0e7749ab
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/2082996Reviewed-by: Rune Lillesveen <futhark@chromium.org>
Commit-Queue: Alison Maher <almaher@microsoft.com>
Cr-Commit-Position: refs/heads/master@{#746412}

third_party/blink/renderer/core/css/parser/css_parser.cc

@@ -259,14 +259,6 @@ bool CSSParser::ParseSystemColor(Color& color,
   if (!StyleColor::IsSystemColor(id))
     return false;
 
-  if (!RuntimeEnabledFeatures::LinkSystemColorsEnabled() &&
-      (id == CSSValueID::kLinktext || id == CSSValueID::kVisitedtext)) {
-    return false;
-  } else if (!RuntimeEnabledFeatures::NewSystemColorsEnabled() &&
-             (id == CSSValueID::kActivetext || id == CSSValueID::kField ||
-              id == CSSValueID::kFieldtext)) {
-    return false;
-  }
   color = LayoutTheme::GetTheme().SystemColor(id, color_scheme);
   return true;
 }

third_party/blink/renderer/core/css/parser/css_property_parser_helpers.cc

@@ -928,15 +928,6 @@ CSSValue* ConsumeColor(CSSParserTokenRange& range,
     if (!isValueAllowedInMode(id, context.Mode()))
       return nullptr;
     CSSIdentifierValue* color = ConsumeIdent(range);
-    if (!RuntimeEnabledFeatures::LinkSystemColorsEnabled() &&
-        (color->GetValueID() == CSSValueID::kLinktext ||
-         color->GetValueID() == CSSValueID::kVisitedtext)) {
-      return nullptr;
-    } else if (!RuntimeEnabledFeatures::NewSystemColorsEnabled() &&
-               (id == CSSValueID::kActivetext || id == CSSValueID::kField ||
-                id == CSSValueID::kFieldtext)) {
-      return nullptr;
-    }
     return color;
   }
   RGBA32 color = Color::kTransparent;

third_party/blink/renderer/platform/runtime_enabled_features.json5

@@ -950,10 +950,6 @@
       name: "LegacyWindowsDWriteFontFallback",
       // Enabled by features::kLegacyWindowsDWriteFontFallback;
     },
-    {
-      name: "LinkSystemColors",
-      status: "stable",
-    },
     {
       name:"ManualSlotting",
       status:"experimental",
@@ -1128,10 +1124,6 @@
     {
       name: "NewRemotePlaybackPipeline",
     },
-    {
-      name: "NewSystemColors",
-      status: "stable",
-    },
     {
       name: "NoIdleEncodingForWebTests",
       status: "test",