Remove "DesktopStudy" suffix from QRCodeGenerator study to match gcl.

Change-Id: I8a68ead67e71e01843dad72681e1e786a313a45e
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/2330298
Commit-Queue: Travis Skare <skare@chromium.org>
Reviewed-by: Robert Kaplow <rkaplow@chromium.org>
Cr-Commit-Position: refs/heads/master@{#794261}

testing/variations/fieldtrial_testing_config.json

@@ -5539,7 +5539,7 @@
             ]
         }
     ],
-    "QRCodeGeneratorDesktopStudy": [
+    "QRCodeGenerator": [
         {
             "platforms": [
                 "chromeos",