Enable CrOSUserSpaceLowMemoryNotification by default

Also delete testing config.

Bug: b/149833548
Change-Id: I314961ff0c037933572b81a909bf792f7678017f
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/2366321Reviewed-by: Brian Geffon <bgeffon@chromium.org>
Reviewed-by: Ilya Sherman <isherman@chromium.org>
Commit-Queue: Kuo-Hsin Yang <vovoy@chromium.org>
Cr-Commit-Position: refs/heads/master@{#801216}

chromeos/memory/pressure/system_memory_pressure_evaluator.cc

@@ -29,7 +29,7 @@ namespace chromeos {
 namespace memory {
 
 const base::Feature kCrOSUserSpaceLowMemoryNotification{
-    "CrOSUserSpaceLowMemoryNotification", base::FEATURE_DISABLED_BY_DEFAULT};
+    "CrOSUserSpaceLowMemoryNotification", base::FEATURE_ENABLED_BY_DEFAULT};
 
 namespace {
 // Pointer to the SystemMemoryPressureEvaluator used by TabManagerDelegate for

testing/variations/fieldtrial_testing_config.json

@@ -1510,21 +1510,6 @@
             ]
         }
     ],
-    "CrOSUserSpaceLowMemoryNotification": [
-        {
-            "platforms": [
-                "chromeos"
-            ],
-            "experiments": [
-                {
-                    "name": "Enabled_20200520",
-                    "enable_features": [
-                        "CrOSUserSpaceLowMemoryNotification"
-                    ]
-                }
-            ]
-        }
-    ],
     "CrostiniWebUIUpgrader": [
         {
             "platforms": [