[ftp] Rename fieldtrial configuration.

The internal configuration name was changed. Update fieldtrial
configuration to match.

Bug: 333943
Change-Id: I70eb78ec4829788d78ef9c925ae2866cd54575d3
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/1929845Reviewed-by: Mark Pearson <mpearson@chromium.org>
Commit-Queue: Asanka Herath <asanka@chromium.org>
Cr-Commit-Position: refs/heads/master@{#718354}

testing/variations/fieldtrial_testing_config.json

@@ -1961,7 +1961,7 @@
             ],
             "experiments": [
                 {
-                    "name": "ForcedOff_FtpProtocol",
+                    "name": "WithoutFtpSupport",
                     "disable_features": [
                         "FtpProtcol"
                     ]