[tint] Remove redundant 'case' statement

Change-Id: I99abe53eafe9ae15323027163067ff1d2861af9f
Reviewed-on: https://dawn-review.googlesource.com/c/dawn/+/150145
Kokoro: Kokoro <noreply+kokoro@google.com>
Reviewed-by: James Price <jrprice@google.com>
Auto-Submit: Ben Clayton <bclayton@google.com>
Commit-Queue: James Price <jrprice@google.com>

src/tint/lang/msl/writer/ast_raise/module_scope_var_to_entry_point_param.cc

diff --git a/src/tint/lang/msl/writer/ast_raise/module_scope_var_to_entry_point_param.cc b/src/tint/lang/msl/writer/ast_raise/module_scope_var_to_entry_point_param.cc
index 105ba58..54531f7 100644
--- a/src/tint/lang/msl/writer/ast_raise/module_scope_var_to_entry_point_param.cc
+++ b/src/tint/lang/msl/writer/ast_raise/module_scope_var_to_entry_point_param.cc
@@ -201,12 +201,6 @@
                 }
                 break;
             }
-            case core::AddressSpace::kPushConstant: {
-                ctx.dst->Diagnostics().add_error(
-                    diag::System::Transform,
-                    "unhandled module-scope address space (" + tint::ToString(sc) + ")");
-                break;
-            }
             default: {
                 TINT_ICE() << "unhandled module-scope address space (" << sc << ")";
                 break;