Revert "[Perf waterfall] Set io_timeout to 4 hours."

This reverts commit 4decd028.

Reason for revert: broke tests.

Original change's description:
> [Perf waterfall] Set io_timeout to 4 hours.
> 
> TBR=simonhatch@chromium.org
> 
> Bug: 969819
> Change-Id: I772891cbfacaae9c6d0c233e2934e54826bec69c
> Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/1639576
> Reviewed-by: Caleb Rouleau <crouleau@chromium.org>
> Commit-Queue: Caleb Rouleau <crouleau@chromium.org>
> Auto-Submit: Caleb Rouleau <crouleau@chromium.org>
> Cr-Commit-Position: refs/heads/master@{#665701}

TBR=simonhatch@chromium.org,crouleau@chromium.org,jbudorick@chromium.org,hypan@google.com

Change-Id: If6163597a4cc2ddf366692109328a6273fdbe98a
No-Presubmit: true
No-Tree-Checks: true
No-Try: true
Bug: 969819
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/1642152Reviewed-by: Caleb Rouleau <crouleau@chromium.org>
Commit-Queue: Caleb Rouleau <crouleau@chromium.org>
Cr-Commit-Position: refs/heads/master@{#665718}

testing/buildbot/chromium.perf.fyi.json

@@ -33,7 +33,7 @@
           "expiration": 7200,
           "hard_timeout": 36000,
           "ignore_task_failure": false,
-          "io_timeout": 14400,
+          "io_timeout": 1800,
           "shards": 3
         },
         "trigger_script": {
@@ -77,7 +77,7 @@
           "expiration": 7200,
           "hard_timeout": 36000,
           "ignore_task_failure": false,
-          "io_timeout": 14400
+          "io_timeout": 1800
         },
         "trigger_script": {
           "args": [

tools/perf/core/perf_data_generator.py

@@ -1084,11 +1084,7 @@ def generate_performance_test(tester_config, test):
     # to ~2 hrs.
     'hard_timeout': 10 * 60 * 60, # 10 hours timeout for full suite
     'ignore_task_failure': False,
-    # 4 hour timeout. Note that this is effectively the timeout for a
-    # benchmarking subprocess to run since we intentionally do not stream
-    # subprocess output to the task stdout.
-    # TODO(crbug.com/865538): Reduce this once we can reduce hard_timeout.
-    'io_timeout': 4 * 60 * 60,
+    'io_timeout': 30 * 60, # 30 minutes
     'dimension_sets': [
       tester_config['dimension']
     ],