security: Remove discussion of how other SaaS providers work.

While from my anecdotal experience, it is accurate that at many SaaS
providers, dozens or even hundreds of engineers have access to
production infrastructure, the "essentially all" statement isn't true
(not sure how that got added), and in any case, there aren't great
public sources we can cite to educate folks who might think Silicon
Valley startup practices are better than they actually are.

templates/zerver/security.md

@@ -131,10 +131,8 @@ the industry:
 - All access to user data (messages, streams, uploaded files, etc.) in the
   Zulip backend is through carefully-audited core libraries that validate
   that the user who is making the request has access to that data.
-- With many SaaS providers, essentially all engineers have direct shell
-  access to production servers storing user data.  Zulip Cloud is different:
-  only a small handful of security-trained engineers have access to
-  production servers or to sensitive customer data.
+- Only a small handful of people have access to production servers or
+  to sensitive customer data.
 - Our error handling systems are have been designed from the beginning to
   avoid including user message content in error reports, even in cases where
   this makes debugging quite difficult (e.g. bugs in the message rendering