Update linux_function_app_resource.go

Latest Azure API changes throws errors if this setting is present in both locations:

```
performing CreateOrUpdate: unexpected status 400 (400 Bad Request) with response: {"Code":"BadRequest","Message":"There was a conflict. SiteConfig.PublicNetworkAccess cannot be modified. Please modify the Site.PublicNetworkAccess property.","Target":null,"Details":[{"Message":"There was a conflict. SiteConfig.PublicNetworkAccess cannot be modified. Please modify the Site.PublicNetworkAccess property."},{"Code":"BadRequest"},{"ErrorEntity":{"ExtendedCode":"01020","MessageTemplate":"There was a conflict. {0}","Parameters":["SiteConfig.PublicNetworkAccess cannot be modified. Please modify the Site.PublicNetworkAccess property."],"Code":"BadRequest","Message":"There was a conflict. SiteConfig.PublicNetworkAccess cannot be modified. Please modify the Site.PublicNetworkAccess property."}}],"Innererror":null}
```

internal/services/appservice/linux_function_app_resource.go

@@ -1039,9 +1039,7 @@ func (r LinuxFunctionAppResource) Update() sdk.ResourceFunc {
 					pna = helpers.PublicNetworkAccessDisabled
 				}
 
-				// (@jackofallops) - Values appear to need to be set in both SiteProperties and SiteConfig for now? https://github.com/Azure/azure-rest-api-specs/issues/24681
 				model.Properties.PublicNetworkAccess = pointer.To(pna)
-				model.Properties.SiteConfig.PublicNetworkAccess = model.Properties.PublicNetworkAccess
 			}
 
 			if err := client.CreateOrUpdateThenPoll(ctx, *id, model); err != nil {