Remove WinServer2008 from CELab host template file (end of support).

Context:
  WinServer2008's end of support on Jan 14th 2020
  https://support.microsoft.com/en-us/lifecycle/search?alpha=windows%20server%202008

Changes:
- Removed Win2008r2 from the template host file used in tests.
  It's not currently used in any chromium tests, so no test to update.

Follow-up to change in enterprise/cel:
  https://crrev.com/c/1936508

Bug: 1028769
Change-Id: I86410c88cdcfbe4e87e2600d1f20fde3638dd80a
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/1937572Reviewed-by: Owen Min <zmin@chromium.org>
Commit-Queue: Mathieu Binette <mbinette@google.com>
Auto-Submit: Mathieu Binette <mbinette@google.com>
Cr-Commit-Position: refs/heads/master@{#721503}

chrome/browser/policy/e2e_test/infra/template.host.textpb

@@ -66,29 +66,6 @@ machine_type {
   }
 }
 
-machine_type {
-  # Name must match the host_machine_type field in the windows_machine asset
-  # entries.
-  name: 'win2008r2'
-
-  instance_properties {
-    machineType: 'projects/${host.project.name}/zones/${host.project.zone}/machineTypes/n1-standard-2'
-
-    scheduling {
-      automaticRestart: true
-    }
-
-    disks {
-      autoDelete: true
-      boot: true
-
-      initializeParams {
-        sourceImage: '${host.image.windows-2008-r2.url}'
-      }
-    }
-  }
-}
-
 machine_type {
   # Name must match the host_machine_type field in the windows_machine asset
   # entries.