[CSS Grid Layout] Remove unused variable in test

LayoutTests/fast/css-grid-layout/implicit-position-dynamic-change.html

Index: LayoutTests/fast/css-grid-layout/implicit-position-dynamic-change.html
diff --git a/LayoutTests/fast/css-grid-layout/implicit-position-dynamic-change.html b/LayoutTests/fast/css-grid-layout/implicit-position-dynamic-change.html
index 16b27cf2b1107db3a4a9fd9a2af0d75f9942a566..db143cebe25fe33250d1e5c71000f988ba8e2de0 100644
--- a/LayoutTests/fast/css-grid-layout/implicit-position-dynamic-change.html
+++ b/LayoutTests/fast/css-grid-layout/implicit-position-dynamic-change.html
@@ -21,7 +21,6 @@ function testPosition(gridElementID, position, size)
 
 function updateImplicitGridColumn()
 {
-    var gridItem = document.getElementById("constrainedGrid").firstChild;
     testPosition("constrainedGrid", { 'column': '1', 'row': '1' }, { 'width': '50', 'height': '70' });
     testPosition("constrainedGrid", { 'column': '1', 'row': '2' }, { 'width': '50', 'height': '30' });
     testPosition("constrainedGrid", { 'column': '1', 'row': '3' }, { 'width': '50', 'height': '50' });
@@ -48,7 +47,6 @@ function updateImplicitGridColumn()
 
     testPosition("constrainedGrid", { 'column': '10', 'row': '15' }, { 'width': '40', 'height': '30' });
 
-    var gridItem = document.getElementById("constrainedGridUndefinedHeight").firstChild;
     testPosition("constrainedGridUndefinedHeight", { 'column': '1', 'row': '1' }, { 'width': '50', 'height': '70' });
     testPosition("constrainedGridUndefinedHeight", { 'column': '1', 'row': '2' }, { 'width': '50', 'height': '70' });
     testPosition("constrainedGridUndefinedHeight", { 'column': '1', 'row': '3' }, { 'width': '50', 'height': '50' });
@@ -75,7 +73,6 @@ function updateImplicitGridColumn()
 
     testPosition("constrainedGridUndefinedHeight", { 'column': '10', 'row': '15' }, { 'width': '40', 'height': '30' });
 
-    gridItem = document.getElementById("unconstrainedGrid").firstChild;
     testPosition("unconstrainedGrid", { 'column': '1', 'row': '1' }, { 'width': '50', 'height': '70' });
     testPosition("unconstrainedGrid", { 'column': '2', 'row': '1' }, { 'width': '60', 'height': '70' });
     testPosition("unconstrainedGrid", { 'column': '3', 'row': '1' }, { 'width': '130', 'height': '70' });