use SK_VULKAN_HEADER pattern

I suspect the rebased path is tripping up GOMA?

Change-Id: If6984fdbd4f3ac1bf673bf810ea28bd16a860175
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/1582043
Commit-Queue: Mike Klein <mtklein@chromium.org>
Commit-Queue: Brian Osman <brianosman@google.com>
Auto-Submit: Mike Klein <mtklein@chromium.org>
Reviewed-by: Brian Osman <brianosman@google.com>
Cr-Commit-Position: refs/heads/master@{#653582}

skia/BUILD.gn

@@ -56,7 +56,7 @@ config("skia_config") {
   defines = [
     "SK_HAS_PNG_LIBRARY",
     "SK_HAS_WEBP_LIBRARY",
-    "SK_USER_CONFIG_HEADER=\"" + rebase_path("config/SkUserConfig.h") + "\"",
+    "SK_USER_CONFIG_HEADER=\"../../skia/config/SkUserConfig.h\"",
   ]
 
   if (!is_ios) {