Remove [[block]] attribute from all shaders

This has been removed from WGSL and is now deprecated in Tint.

Bug: tint:1324
Change-Id: Ic187ce3c5ce0723db6f3ca6483e9f5e73ce27acc
Reviewed-on: https://dawn-review.googlesource.com/c/dawn/+/72880
Auto-Submit: James Price <jrprice@google.com>
Reviewed-by: Corentin Wallez <cwallez@google.com>
Reviewed-by: Corentin Wallez <cwallez@chromium.org>
Commit-Queue: Corentin Wallez <cwallez@chromium.org>

examples/Animometer.cpp

@@ -58,7 +58,7 @@ void init() {
                         640, 480);
 
     wgpu::ShaderModule vsModule = utils::CreateShaderModule(device, R"(
-        [[block]] struct Constants {
+        struct Constants {
             scale : f32;
             time : f32;
             offsetX : f32;

examples/ComputeBoids.cpp

@@ -151,7 +151,7 @@ void initSim() {
             pos : vec2<f32>;
             vel : vec2<f32>;
         };
-        [[block]] struct SimParams {
+        struct SimParams {
             deltaT : f32;
             rule1Distance : f32;
             rule2Distance : f32;
@@ -161,7 +161,7 @@ void initSim() {
             rule3Scale : f32;
             particleCount : u32;
         };
-        [[block]] struct Particles {
+        struct Particles {
             particles : array<Particle>;
         };
         [[binding(0), group(0)]] var<uniform> params : SimParams;