Disable fieldtrial config for FontSrcLocalMatching on Windows

Disable this configuration until bot testing stability issues are
addressed.

Bug: 999787
Change-Id: I82f3803d9def9ca13fbf991a1752d0e384024552
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/1778613
Auto-Submit: Dominik Röttsches <drott@chromium.org>
Reviewed-by: Etienne Bergeron <etienneb@chromium.org>
Reviewed-by: Steven Holte <holte@chromium.org>
Commit-Queue: Dominik Röttsches <drott@chromium.org>
Cr-Commit-Position: refs/heads/master@{#692965}

testing/variations/fieldtrial_testing_config.json

@@ -2447,8 +2447,7 @@
                 "android_webview",
                 "chromeos",
                 "linux",
-                "mac",
-                "windows"
+                "mac"
             ],
             "experiments": [
                 {