Update validate-arc.mdx

At least how we initially designed it, spec validation is opt in as well - i am not aware if that changed but ignore if that's the case

src/content/docs/guides/validate-arc.mdx

@@ -29,12 +29,6 @@ import { Card } from '@astrojs/starlight/components';
     </Steps>
 </Card>
 
-
-:::note
-By default every ARC is validated against the "ARC specification" to guarantee ARC intactness.
-:::
-
-
 ## Check the validation results
 
 <Card icon="gitlab" title="PLANTDataHUB">
@@ -50,4 +44,4 @@ By default every ARC is validated against the "ARC specification" to guarantee A
 
 :::tip
 Find out more about ARC validation [here](/nfdi4plants.knowledgebase/arc-validation/cqc-pipelines/)
-:::
+:::