Revert "Add a temporary requirement for Mac bots to have XCode."

This reverts commit d3c4eda135a1b1930641f7b2a0b417cf9d1cc7e3.

Reason for revert: Issue has been fixed so we can remove the XCode
requirement.

Original change's description:
> Add a temporary requirement for Mac bots to have XCode.
> 
> BUG=chromium:884015
> 
> Change-Id: Iee2373b23ab5534165b36c40600cae86545ee3d9
> Reviewed-on: https://dawn-review.googlesource.com/1544
> Reviewed-by: Kai Ninomiya <kainino@chromium.org>
> Reviewed-by: Stephen White <senorblanco@chromium.org>

TBR=cwallez@chromium.org,kainino@chromium.org,senorblanco@chromium.org

# Not skipping CQ checks because original CL landed > 1 day ago.

Bug: chromium:884015
Change-Id: I5ae40e2343c7684bdbe533f5a8baa1490cdb37d1
Reviewed-on: https://dawn-review.googlesource.com/1643
Reviewed-by: Corentin Wallez <cwallez@chromium.org>
Commit-Queue: Corentin Wallez <cwallez@chromium.org>
diff --git a/infra/config/global/cr-buildbucket.cfg b/infra/config/global/cr-buildbucket.cfg
index 611ae0c..1c78612 100644
--- a/infra/config/global/cr-buildbucket.cfg
+++ b/infra/config/global/cr-buildbucket.cfg
@@ -124,15 +124,11 @@
       name: "mac-dbg"
       dimensions: "os:Mac-10.13"
       mixins: "debug"
-      # Require XCode temporarily to avoid https://crbug.com/884015
-      dimensions: "xcode_version:9.3"
     }
     builders {
       name: "mac-rel"
       dimensions: "os:Mac-10.13"
       mixins: "release"
-      # Require XCode temporarily to avoid https://crbug.com/884015
-      dimensions: "xcode_version:9.3"
     }
 
     # Linux: test combinations of {clang,msvc}x{release,debug}x{x86,x64}
@@ -254,16 +250,12 @@
       name: "mac-dbg"
       dimensions: "os:Mac-10.13"
       mixins: "debug"
-      # Require XCode temporarily to avoid https://crbug.com/884015
-      dimensions: "xcode_version:9.3"
     }
     # Actually on the CQ
     builders {
       name: "mac-rel"
       dimensions: "os:Mac-10.13"
       mixins: "release"
-      # Require XCode temporarily to avoid https://crbug.com/884015
-      dimensions: "xcode_version:9.3"
     }
 
     # Actually on the CQ