No bug - Mark variable-substitution-variable-declaration.html as passing on stylo after servo PR 18660 a=bustage

MozReview-Commit-ID: BURWYVI1vFO

--HG--
extra : rebase_source : 2b7f2fedd440db25786cc3f3d07e593edb00b318

testing/web-platform/meta/css/css-variables-1/variable-substitution-variable-declaration.html.ini

@@ -1,6 +0,0 @@
-[variable-substitution-variable-declaration.html]
-  type: testharness
-  [target10 --varC]
-    expected:
-      if stylo: FAIL
-