Disable allowMerchantAIAPIKey flag in all builds (#15421)

Author: iamgabrielma

Experiments/Experiments/DefaultFeatureFlagService.swift

@@ -98,7 +98,7 @@ public struct DefaultFeatureFlagService: FeatureFlagService {
         case .notificationSettings:
             return true
         case .allowMerchantAIAPIKey:
-            return buildConfig == .localDeveloper || buildConfig == .alpha
+            return false
         default:
             return true
         }