Revert "Add a guard for MTLDevice.counterSets being null."

This reverts commit 610f184fd9.

Reason for revert: Crashes still happen even with this guard.
Testing shows that counterSets being null does not cause crashes.

Original change's description:
> Add a guard for MTLDevice.counterSets being null.
>
> This is a tentative fix for a segfault that's happening on
> metal::Adapter initialization on some systems.
>
> Bug: dawn:1102
> Change-Id: Iff31e46420e60cd76ecbbfa92bd5b5906ca89cf4
> Reviewed-on: https://dawn-review.googlesource.com/c/dawn/+/69340
> Auto-Submit: Corentin Wallez <cwallez@chromium.org>
> Commit-Queue: Austin Eng <enga@chromium.org>
> Reviewed-by: Austin Eng <enga@chromium.org>

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

Bug: dawn:1102
Change-Id: Ia7d7428acee552a107425c774ba15e97bf170e38
Reviewed-on: https://dawn-review.googlesource.com/c/dawn/+/71241
Reviewed-by: Jiawei Shao <jiawei.shao@intel.com>
Commit-Queue: Austin Eng <enga@chromium.org>

src/dawn_native/metal/BackendMTL.mm

@@ -194,14 +194,12 @@ namespace dawn_native { namespace metal {
             // MTLDevice’s counterSets property declares which counter sets it supports. Check
             // whether it's available on the device before requesting a counter set.
             id<MTLCounterSet> counterSet = nil;
-            if (device.counterSets != nil) {
             for (id<MTLCounterSet> set in device.counterSets) {
                 if ([set.name caseInsensitiveCompare:counterSetName] == NSOrderedSame) {
                     counterSet = set;
                     break;
                 }
             }
-            }
 
             // The counter set is not supported.
             if (counterSet == nil) {