[test] Remove duplicated traces from the JSTests3 config

TBR=machenbach@chromium.org

Bug: chromium:880724
Change-Id: I6006bb642cab4e9dfcfb4cba43eeb959fe01f046
Reviewed-on: https://chromium-review.googlesource.com/c/v8/v8/+/1584327
Commit-Queue: Sergiy Belozorov <sergiyb@chromium.org>
Reviewed-by: Sergiy Belozorov <sergiyb@chromium.org>
Cr-Commit-Position: refs/heads/master@{#61025}

test/js-perf-test/JSTests3.json

@@ -222,10 +222,7 @@
             {"name": "StringDropLastSubstring"},
             {"name": "StringTakeLastSlice"},
             {"name": "StringTakeLastSubstr"},
-            {"name": "StringTakeLastSubstring"},
-            {"name": "StringDropFirstSlice"},
-            {"name": "StringDropFirstSubstr"},
-            {"name": "StringDropFirstSubstring"}
+            {"name": "StringTakeLastSubstring"}
           ]
         }
       ]