tests: Stop using the [[block]] attribute

This has been deprecated and will soon be removed.

Bug: tint:1324
Change-Id: If5dbbc3a40d7591591fb2802dbe9c8dd5f96d299
Reviewed-on: https://dawn-review.googlesource.com/c/tint/+/72087
Reviewed-by: Ben Clayton <bclayton@google.com>
Kokoro: Kokoro <noreply+kokoro@google.com>

test/vk-gl-cts/graphicsfuzz/cov-increment-int-loop-counter-mod-array/0-opt.wgsl

@@ -1,6 +1,5 @@
 type Arr = [[stride(16)]] array<i32, 5>;
 
-[[block]]
 struct buf0 {
   x_GLF_uniform_int_values : Arr;
 };