[infra/config] switch to xenial builderless android cfi builder

Bots are added in
https://chrome-internal-review.googlesource.com/c/infradata/config/+/1387683

TBR=jbudorick

Bug: 954450, 956776
Change-Id: I1444fd2b196e10310abc449d965a7213b81deecc
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/1661319Reviewed-by: Takuto Ikuta <tikuta@chromium.org>
Commit-Queue: Takuto Ikuta <tikuta@chromium.org>
Cr-Commit-Position: refs/heads/master@{#669592}

infra/config/cr-buildbucket.cfg

@@ -2834,12 +2834,13 @@ buckets {
     }
     builders {
       name: "Android CFI"
-      dimensions: "os:Ubuntu-14.04"
       dimensions: "cores:32"
       # TODO(https://crbug.com/919430) Remove the larger timeout once compile
       # times have been brought down to reasonable level
       execution_timeout_secs: 16200  # 4.5h
       mixins: "memory-ci-goma-rbe-prod"
+      mixins: "linux-xenial"
+      mixins: "builderless"
     }
     builders {
       name: "chromeos-amd64-generic-rel-goma-canary"
@@ -4496,10 +4497,11 @@ buckets {
     }
     builders {
       name: "android_cfi_rel_ng"
-      dimensions: "os:Ubuntu-14.04"
       dimensions: "cores:32"
       mixins: "android-try"
       mixins: "goma-rbe-prod"
+      mixins: "linux-xenial"
+      mixins: "builderless"
     }
     builders {
       name: "android_mojo"