delete unnecessary style

src/client/styles/scss/_override-handsontable.scss

@@ -1,3 +0,0 @@
-.modal .handsontable .wtBorder {
-  z-index: 110;
-}

src/client/styles/scss/style.scss

@@ -14,9 +14,6 @@
 // override react-bootstrap-typeahead styles
 @import 'override-rbt';
 
-// override Handsontable styles
-@import 'override-handsontable';
-
 // crowi component
 @import 'admin';
 @import 'attachments';