[turbolizer] Hide the '+' tabs that do nothing

They have no function and are confusing to first time users, who think
that you have to click that to upload a file.

It would be better to not add them at all, but the logic searches for
'li.last-tab' and it seems hard to unravel.

Bug: v8:7327
Notry: true
Change-Id: I07e903947e15ccc0d5431488a4c4fcded999f91d
Reviewed-on: https://chromium-review.googlesource.com/c/v8/v8/+/1863194
Commit-Queue: Sigurd Schneider <sigurds@chromium.org>
Reviewed-by: Sigurd Schneider <sigurds@chromium.org>
Cr-Commit-Position: refs/heads/master@{#64325}

tools/turbolizer/turbo-visualizer.css

@@ -697,6 +697,10 @@ text {
   outline: 1px dotted grey;
 }
 
+.last-tab {
+  display: none !important;
+}
+
 ul.disassembly-list .block-id {
   width: 4ex;
   display: block;