[js-perf-test] Don't run SixSpeed benchmarks with --future.

Change-Id: I187cf2f5cffa48ea4eb3d137260fd6dc555b1ed5
Reviewed-on: https://chromium-review.googlesource.com/974404Reviewed-by: Michael Hablich <hablich@chromium.org>
Commit-Queue: Benedikt Meurer <bmeurer@chromium.org>
Cr-Commit-Position: refs/heads/master@{#52129}

test/js-perf-test/SixSpeed.json

@@ -93,7 +93,6 @@
     {
       "name": "Spread",
       "path": ["SixSpeed"],
-      "flags": ["--future"],
       "results_regexp": "^%s\\(Score\\): (.+)$",
       "tests": [
         {
@@ -144,7 +143,6 @@
     {
       "name": "SuperSpread",
       "path": ["SixSpeed"],
-      "flags": ["--future"],
       "results_regexp": "^%s\\(Score\\): (.+)$",
       "tests": [
         {
@@ -170,7 +168,6 @@
     {
       "name": "SpreadLiteral",
       "path": ["SixSpeed"],
-      "flags": ["--future"],
       "results_regexp": "^%s\\(Score\\): (.+)$",
       "tests": [
         {