tint/writer/msl: Remove TODO and old logic

crbug.com/tint/1580 has been implemented for some time.
Remove the bodge to handle constant value lets.

Bug: tint:1580
Change-Id: I9a71ed8f91b6c9925fa0557bcb4c95d90461421f
Reviewed-on: https://dawn-review.googlesource.com/c/dawn/+/99704
Commit-Queue: Antonio Maiorano <amaiorano@google.com>
Kokoro: Kokoro <noreply+kokoro@google.com>
Commit-Queue: Ben Clayton <bclayton@google.com>
Auto-Submit: Ben Clayton <bclayton@google.com>
Reviewed-by: Antonio Maiorano <amaiorano@google.com>
diff --git a/src/tint/writer/msl/generator_impl.cc b/src/tint/writer/msl/generator_impl.cc
index 602ec71..cccf622 100644
--- a/src/tint/writer/msl/generator_impl.cc
+++ b/src/tint/writer/msl/generator_impl.cc
@@ -1764,14 +1764,8 @@
 
 bool GeneratorImpl::EmitExpression(std::ostream& out, const ast::Expression* expr) {
     if (auto* sem = builder_.Sem().Get(expr)) {
-        if (auto* user = sem->As<sem::VariableUser>();
-            !user || !user->Variable()->Declaration()->Is<ast::Let>()) {
-            // Disable constant inlining if the constant expression is from a 'let' declaration.
-            // TODO(crbug.com/tint/1580): Once 'const' is implemented, 'let' will no longer resolve
-            // to a shader-creation time constant value, and this can be removed.
-            if (auto constant = sem->ConstantValue()) {
-                return EmitConstant(out, constant);
-            }
+        if (auto constant = sem->ConstantValue()) {
+            return EmitConstant(out, constant);
         }
     }
     return Switch(