Remove custom getter for outline-offset

We fixed a bug in "outline-offset" computed style at r755943.
This is just a follow-up patch to remove the custom getter
from ComputedStyle as it's not longer needed.

Bug: 1005372
Change-Id: I5bb76ee60444fc772a0a95139f6fd16b25604bc1
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/2134144Reviewed-by: Rune Lillesveen <futhark@chromium.org>
Commit-Queue: Manuel Rego <rego@igalia.com>
Cr-Commit-Position: refs/heads/master@{#756220}

third_party/blink/renderer/core/css/css_properties.json5

@@ -2634,7 +2634,6 @@
       field_template: "primitive",
       default_value: "0",
       type_name: "int",
-      computed_style_custom_functions: ["getter"],
       converter: "ConvertComputedLength<int>",
       typedom_types: ["Length"],
       valid_for_cue: true,

third_party/blink/renderer/core/style/computed_style.h

@@ -707,7 +707,7 @@ class ComputedStyle : public ComputedStyleBase,
            OutlineColorIsCurrentColor() == other.OutlineColorIsCurrentColor() &&
            OutlineColor() == other.OutlineColor() &&
            OutlineStyle() == other.OutlineStyle() &&
-           OutlineOffsetInternal() == other.OutlineOffsetInternal() &&
+           OutlineOffset() == other.OutlineOffset() &&
            OutlineStyleIsAuto() == other.OutlineStyleIsAuto();
   }
 
@@ -727,11 +727,6 @@ class ComputedStyle : public ComputedStyleBase,
   }
   void SetOutlineWidth(uint16_t v) { SetOutlineWidthInternal(LayoutUnit(v)); }
 
-  // outline-offset
-  int OutlineOffset() const {
-    return OutlineOffsetInternal();
-  }
-
   // -webkit-perspective-origin-x
   const Length& PerspectiveOriginX() const { return PerspectiveOrigin().X(); }
   void SetPerspectiveOriginX(const Length& v) {