Revert "Enable "AsyncDns" feature by default on Android"

This reverts commit 0532f223eac50c7aee9677bf499ba6c5c182a41f.

Reason for revert: Full launch needs to be rolled back and retried in a future milestone due to a bug. The experiment cleanup here was premature.

Original change's description:
> Enable "AsyncDns" feature by default on Android
> 
> Also clean up Android-specific experiment code, but leave the
> base::Feature.
> 
> Bug: 768874
> Change-Id: Ic7b81a878e3e81bc1a5c2c2fae242df23c5387ca
> Reviewed-on: https://chromium-review.googlesource.com/868077
> Reviewed-by: Ilya Sherman <[email protected]>
> Commit-Queue: Miriam Gershenson <[email protected]>
> Cr-Commit-Position: refs/heads/master@{#529866}

[email protected],[email protected]

# Not skipping CQ checks because original CL landed > 1 day ago.

Bug: 768874, 805020
Change-Id: Ib67c727aef748b4e80714e6128c3bfbdc24d3544
Reviewed-on: https://chromium-review.googlesource.com/881206
Reviewed-by: Miriam Gershenson <[email protected]>
Commit-Queue: Miriam Gershenson <[email protected]>
Cr-Commit-Position: refs/heads/master@{#531381}
diff --git a/chrome/browser/flag_descriptions.h b/chrome/browser/flag_descriptions.h
index 3c52bac..b34b428 100644
--- a/chrome/browser/flag_descriptions.h
+++ b/chrome/browser/flag_descriptions.h
@@ -1035,6 +1035,9 @@
 extern const char kAndroidViewPasswordsName[];
 extern const char kAndroidViewPasswordsDescription[];
 
+extern const char kAsyncDnsName[];
+extern const char kAsyncDnsDescription[];
+
 extern const char kAutofillAccessoryViewName[];
 extern const char kAutofillAccessoryViewDescription[];