[cr-buildbucket.cfg] Update dimensions for Mac deterministic / dbg

4 core -> 24 core.

Bug: 790381, 790383
TBR: tandrii
Change-Id: I1f80d45bddd904fc186a00cd1db50f436770173d
Reviewed-on: https://chromium-review.googlesource.com/1110998Reviewed-by: Ryan Tseng <hinoka@chromium.org>
Reviewed-by: Andrii Shyshkalov <tandrii@chromium.org>
Commit-Queue: Ryan Tseng <hinoka@chromium.org>
Cr-Commit-Position: refs/heads/master@{#569435}

infra/config/global/cr-buildbucket.cfg

@@ -1738,7 +1738,7 @@ buckets {
     builders {
       name: "Mac deterministic"
       dimensions: "os:Mac-10.13"
-      dimensions: "cores:4"
+      dimensions: "cores:"
       mixins: "fyi-ci"
       mixins: "deterministic"
     }
@@ -1818,7 +1818,7 @@ buckets {
     builders {
       name: "Mac deterministic (dbg)"
       dimensions: "os:Mac-10.13"
-      dimensions: "cores:4"
+      dimensions: "cores:"
       mixins: "fyi-ci"
       mixins: "deterministic"
     }