Remove conditional for X-CS and X-Subdomain check for Vary:.

* X-CS and X-Subdomain should be added to Vary: header for 301s,
keeping in the spirit of idempotent URLs.

Change-Id: Ic830fe37f4ef1372bff0a7d6ac8cb41ff79339cd
Merge "Remove conditional for X-CS and X-Subdomain check for Vary:."