Fix syntax tree build.

The `EmitBinaryOp` method fully covers, so the `default` at the end
triggers a warning about a fully covered switch with a default.

Change-Id: I256bd96770e79afd071b09dd26b3f3d8205ea651
Reviewed-on: https://dawn-review.googlesource.com/c/dawn/+/145441
Kokoro: Kokoro <noreply+kokoro@google.com>
Commit-Queue: Dan Sinclair <dsinclair@chromium.org>
Reviewed-by: Ben Clayton <bclayton@google.com>
diff --git a/src/tint/lang/wgsl/writer/syntax_tree_printer/syntax_tree_printer.cc b/src/tint/lang/wgsl/writer/syntax_tree_printer/syntax_tree_printer.cc
index d2e27f5..16735f2 100644
--- a/src/tint/lang/wgsl/writer/syntax_tree_printer/syntax_tree_printer.cc
+++ b/src/tint/lang/wgsl/writer/syntax_tree_printer/syntax_tree_printer.cc
@@ -725,9 +725,6 @@
         case core::BinaryOp::kModulo:
             Line() << "%";
             break;
-        default:
-            diagnostics_.add_error(diag::System::Writer, "missing binary operation type");
-            break;
     }
 }