Disable flaky performance_browser_tests on win8

BUG=475940
TBR=hubbe@chromium.org, simonhatch@chromium.org

Review URL: https://codereview.chromium.org/1110663002

Cr-Commit-Position: refs/heads/master@{#327097}

testing/buildbot/chromium.perf.json

@@ -337,18 +337,6 @@
     ]
   },
   "Win 8 Perf (2)": {
-    "scripts": [
-      {
-        "args": [
-          "performance_browser_tests",
-          "--test-launcher-print-test-stdio=always",
-          "--gtest_filter=TabCapturePerformanceTest.*:CastV2PerformanceTest.*",
-          "--test-launcher-jobs=1",
-          "--enable-gpu"
-        ],
-        "name": "performance_browser_tests",
-        "script": "gtest_perf_test.py"
-      }
-    ]
+    "scripts": []
   }
 }