Doc: Removed references to beta version

Signed-off-by: Minos Galanakis <minos.galanakis@arm.com>
diff --git a/doxygen/input/doc_mainpage.h b/doxygen/input/doc_mainpage.h
index c1d0f36..4eda5ba 100644
--- a/doxygen/input/doc_mainpage.h
+++ b/doxygen/input/doc_mainpage.h
@@ -10,7 +10,7 @@
  */
 
 /**
- * @mainpage Mbed TLS v4.0.0-beta API Documentation
+ * @mainpage Mbed TLS v4.0.0 API Documentation
  *
  * This documentation describes the application programming interface (API)
  * of Mbed TLS.