[EmojiSuggest] Update field trial param

Rolling out map4 to 1% stable in http://cl/335531678

Bug: b/166523259
Change-Id: Ie5de747bc3c56d12f5425083de5f2c245cc6f9ef
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/2449656Reviewed-by: Jesse Doherty <jwd@chromium.org>
Commit-Queue: My Nguyen <myy@chromium.org>
Cr-Commit-Position: refs/heads/master@{#814365}

testing/variations/fieldtrial_testing_config.json

@@ -1448,9 +1448,9 @@
             ],
             "experiments": [
                 {
-                    "name": "UseMap2_20200922",
+                    "name": "UseMap4_20200922",
                     "params": {
-                        "map": "2"
+                        "map": "4"
                     },
                     "enable_features": [
                         "EmojiSuggestAddition"