[tint] do not emit space for binding group 0

D3D11 only supports HLSL SM5.0 which doesn't support `space`
(binding group in WGSL). So for D3D11, only one binding group will be
used, and tint will not emit `space` for HLSL, so shaders can be used
with D3D11.

Bug: dawn:1705
Change-Id: Ie0e9868137f10762c5243e188d76f5e41879c2bc
Reviewed-on: https://dawn-review.googlesource.com/c/dawn/+/125080
Commit-Queue: Peng Huang <penghuang@chromium.org>
Reviewed-by: Ben Clayton <bclayton@google.com>
Kokoro: Ben Clayton <bclayton@google.com>
diff --git a/test/tint/builtins/gen/literal/atomicSub/051100.wgsl.expected.dxc.hlsl b/test/tint/builtins/gen/literal/atomicSub/051100.wgsl.expected.dxc.hlsl
index ffa7a8d..67b6e9d 100644
--- a/test/tint/builtins/gen/literal/atomicSub/051100.wgsl.expected.dxc.hlsl
+++ b/test/tint/builtins/gen/literal/atomicSub/051100.wgsl.expected.dxc.hlsl
@@ -1,4 +1,4 @@
-RWByteAddressBuffer sb_rw : register(u0, space0);
+RWByteAddressBuffer sb_rw : register(u0);
 
 int sb_rwatomicSub(uint offset, int value) {
   int original_value = 0;