Update configure-custom-domain.md

In practice, key pinning is obsolete and shouldn't be suggested as "more secure."
Let's remove that "more secure" inference, and just point out that key pinning isn't compatible with a "managed certificate" where the CA root and chain might change.  

Obsolete = https://en.wikipedia.org/wiki/HTTP_Public_Key_Pinning#Certificate_pinning
Less secure = https://security.stackexchange.com/questions/29988/what-is-certificate-pinning

Related to PR = #91084

Author: TroyWitthoeft

articles/api-management/configure-custom-domain.md

@@ -58,7 +58,7 @@ There are several API Management endpoints to which you can assign a custom doma
 API Management supports custom TLS certificates or certificates imported from Azure Key Vault. You can also enable a free, managed certificate.
 
 > [!WARNING]
-> If you wish to improve the security of your applications with certificate pinning, you should use a custom domain name and either a custom or Key Vault certificate, not the default certificate or the free, managed certificate. We don't recommend taking a hard dependency on a certificate that you don't manage.
+> If you require certificate pinning, please use a custom domain name and either a custom or Key Vault certificate, not the default certificate or the free, managed certificate. We don't recommend taking a hard dependency on a certificate that you don't manage.
 
 # [Custom](#tab/custom)