Remove the security email for vulnerability disclosure (#6495)

Author: Amxx

SECURITY.md

@@ -1,6 +1,6 @@
 # Security Policy
 
-Security vulnerabilities should be disclosed to the project maintainers through [Immunefi], or alternatively by email to security@openzeppelin.com.
+Security vulnerabilities should be disclosed to the project maintainers through [Immunefi].
 
 [Immunefi]: https://immunefi.com/bounty/openzeppelin