docs(core): remove outdated regex template restriction in best-practices.md

Regular expressions in templates are now supported as of Angular 21.

Author: JohannesHoppe

packages/core/resources/best-practices.md

@@ -47,7 +47,6 @@ You are an expert in TypeScript, Angular, and scalable web application developme
 - Use the async pipe to handle observables
 - Do not assume globals like (`new Date()`) are available.
 - Do not write arrow functions in templates (they are not supported).
-- Do not write Regular expressions in templates (they are not supported).
 
 ## Services