fix(admin): drop initial applyVisibility and Razor fallback on cohort Edit

The server now renders the hidden attribute on initial load for every Edit
scenario (locked, unlocked, churn-only, migration), so the page-load script
no longer needs the Razor-rendered MigrationPathSelection constant or the
initial applyVisibility call. Keeps only the change listener for interactive
toggling on the unlocked path.

Author: kdenney

src/Admin/Billing/Views/OrganizationPlanMigrationCohorts/Edit.cshtml

@@ -101,8 +101,6 @@
                 churnOptionalLabel.hidden = isChurnOnly;
             };
 
-            const initialValue = select ? select.value : '@Model.FormModel.MigrationPathSelection';
-            applyVisibility(initialValue);
             select?.addEventListener('change', (e) => applyVisibility(e.target.value));
         })();
     </script>