[Cleanup] Remove the obsolete variations_seed pref.

components/variations/pref_names.cc

Index: components/variations/pref_names.cc
diff --git a/components/variations/pref_names.cc b/components/variations/pref_names.cc
index 8bd52ce045a2576ec8cdd176bec954d4fc183899..52d187f3d9a74c0b27d6e65901b698e7926531c3 100644
--- a/components/variations/pref_names.cc
+++ b/components/variations/pref_names.cc
@@ -32,9 +32,6 @@ const char kVariationsPermutedEntropyCache[] =
 // String for the restrict parameter to be appended to the variations URL.
 const char kVariationsRestrictParameter[] = "variations_restrict_parameter";
 
-// Base64-encoded serialized form of the variations seed protobuf.
-const char kVariationsSeed[] = "variations_seed";
-
 // 64-bit integer serialization of the base::Time from the last seed received.
 const char kVariationsSeedDate[] = "variations_seed_date";