ResourceLoadScheduler: remove stale configurations

Remove the entry "Enabled_bg_limit_8", that was for the first field trial.
Also, remove "ReportRendererPeakMemoryStats" feature, that is not
planned to be used in a launching configuration, but it was just for
gathering memory metrics until Beta.

Bug: 775849
Change-Id: Ib496db8d69b6891915cfab453ad4abc13d66e522
Reviewed-on: https://chromium-review.googlesource.com/956945Reviewed-by: Ilya Sherman <isherman@chromium.org>
Commit-Queue: Ilya Sherman <isherman@chromium.org>
Cr-Commit-Position: refs/heads/master@{#542275}

testing/variations/fieldtrial_testing_config.json

@@ -3034,17 +3034,6 @@
                         "bg_sub_limit": "4"
                     },
                     "enable_features": [
-                        "ReportRendererPeakMemoryStats",
-                        "ResourceLoadScheduler"
-                    ]
-                },
-                {
-                    "name": "Enabled_bg_limit_8",
-                    "params": {
-                        "bg_limit": "8"
-                    },
-                    "enable_features": [
-                        "ReportRendererPeakMemoryStats",
                         "ResourceLoadScheduler"
                     ]
                 }