Remove IPH_NewTab from the field trial testing config.

The IPH_NewTab feature no longer appears to be used in the code.

Bug: 1126640
Change-Id: Ia74ecf49241aefd99cb4fd2b95f03cad2575ded3
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/2427353
Commit-Queue: Caitlin Fischer <caitlinfischer@google.com>
Reviewed-by: Ilya Sherman <isherman@chromium.org>
Cr-Commit-Position: refs/heads/master@{#810310}

testing/variations/fieldtrial_testing_config.json

@@ -4547,31 +4547,6 @@
             ]
         }
     ],
-    "NewTabInProductHelp": [
-        {
-            "platforms": [
-                "linux",
-                "windows"
-            ],
-            "experiments": [
-                {
-                    "name": "Enabled_1",
-                    "params": {
-                        "availability": "any",
-                        "event_new_tab_session_time_met": "name:new_tab_session_time_met;comparator:>=1;window:3650;storage:3650",
-                        "event_omnibox_used": "name:omnibox_used;comparator:>=1;window:3650;storage:3650",
-                        "event_trigger": "name:new_tab_trigger;comparator:==0;window:3650;storage:3650",
-                        "event_used": "name:new_tab_opened;comparator:==0;window:3650;storage:3650",
-                        "session_rate": "<0",
-                        "x_promo_string": "0"
-                    },
-                    "enable_features": [
-                        "IPH_NewTab"
-                    ]
-                }
-            ]
-        }
-    ],
     "NewUsbBackend": [
         {
             "platforms": [