Disabled the gpu_times.gpu_rasterization.top_25_smooth perf benchmark for flakiness

NOTRY=true
TBR=dyen@chromium.org
BUG=453131

Review URL: https://codereview.chromium.org/896583004

Cr-Commit-Position: refs/heads/master@{#314264}

tools/perf/benchmarks/gpu_times.py

@@ -57,6 +57,7 @@ class GPUTimesTop25Sites(_GPUTimes):
   def Name(cls):
     return 'gpu_times.top_25_smooth'
 
+@benchmark.Disabled
 class GPUTimesGpuRasterizationTop25Sites(_GPUTimes):
   """Measures GPU timeline metric for the top 25 sites with GPU rasterization.
   """