Fix Field Trial testing config for DnsHttpssvc experiment.

The prior CL put experiment group names in the place where feature param
names should go.

Bug: 1052476
Change-Id: I5ec9f0a8eb6a40a4a570adb626082af53771597d
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/2323140Reviewed-by: Robert Kaplow <rkaplow@chromium.org>
Commit-Queue: Dan McArdle <dmcardle@chromium.org>
Cr-Commit-Position: refs/heads/master@{#792426}

testing/variations/fieldtrial_testing_config.json

@@ -2297,8 +2297,7 @@
                 {
                     "name": "DnsHttpssvcStudy",
                     "params": {
-                        "HttpssvcQueryHttpssvc": "false",
-                        "HttpssvcQueryIntegrity": "true"
+                        "DnsHttpssvcUseIntegrity": "true"
                     },
                     "enable_features": [
                         "DnsHttpssvc"