Remove deprecated SetIndexBuffer (without format).

This also simplifies a bunch of code in backends that was used to handle
getting the indexFormat from the pipeline "late".

Bug: dawn:502

Change-Id: Ibae50c8df21323fd391515f6036552e9fb868d93
Reviewed-on: https://dawn-review.googlesource.com/c/dawn/+/32023
Commit-Queue: Corentin Wallez <cwallez@chromium.org>
Reviewed-by: Austin Eng <enga@chromium.org>
Reviewed-by: Stephen White <senorblanco@chromium.org>
diff --git a/dawn.json b/dawn.json
index d89db56..e00a9af 100644
--- a/dawn.json
+++ b/dawn.json
@@ -1150,6 +1150,7 @@
                 "name": "set index buffer",
                 "args": [
                     {"name": "buffer", "type": "buffer"},
+                    {"name": "format", "type": "index format"},
                     {"name": "offset", "type": "uint64_t", "default": "0"},
                     {"name": "size", "type": "uint64_t", "default": "0"}
                 ]
@@ -1349,6 +1350,7 @@
                 "name": "set index buffer",
                 "args": [
                     {"name": "buffer", "type": "buffer"},
+                    {"name": "format", "type": "index format"},
                     {"name": "offset", "type": "uint64_t", "default": "0"},
                     {"name": "size", "type": "uint64_t", "default": "0"}
                 ]