fix: remove @SInCE marker from hidden attribute (added before provider v2.0)

The hidden attribute for coder_app was added in September 2024, before
terraform-provider-coder v2.0.1 was released in December 2024. Only
resources/features added after provider v2.0 should have @SInCE markers.

Co-authored-by: matifali <[email protected]>

Author: blink-so[bot]

provider/app.go

@@ -251,7 +251,7 @@ func appResource() *schema.Resource {
 			},
 			"hidden": {
 				Type:        schema.TypeBool,
-				Description: "Determines if the app is visible in the UI. @since:v2.16.0",
+				Description: "Determines if the app is visible in the UI.",
 				Default:     false,
 				ForceNew:    true,
 				Optional:    true,