🔥 Remove "openssl extensions must be installed"

"openssl" has been a default gem for a long time.  Although some
installations may still disable it, this is very rare and not important
enough to document here any more.

Looking at "net-http" and "net-smtp", neither of them still document the
scenario where "openssl" is missing.  Although it carefully avoids an
implicit dependency, "net-http" doesn't try to catch any LoadError when
an SSL connection is explicitly used.

Author: nevans

lib/net/imap.rb

@@ -209,12 +209,6 @@ module Net
   #    MOVE Extension", RFC-6851[https://tools.ietf.org/html/rfc6851], January
   #    2013.
   #
-  # [[OSSL]]
-  #    http://www.openssl.org
-  #
-  # [[RSSL]]
-  #    http://savannah.gnu.org/projects/rubypki
-  #
   # [[UTF7[https://tools.ietf.org/html/rfc2152]]]
   #    Goldsmith, D. and Davis, M., "UTF-7: A Mail-Safe Transformation Format of
   #    Unicode", RFC-2152[https://tools.ietf.org/html/rfc2152], May 1997.
@@ -1143,9 +1137,7 @@ def idle_done
     #
     # port::  Port number (default value is 143 for imap, or 993 for imaps)
     # ssl::   If +options[:ssl]+ is true, then an attempt will be made
-    #         to use SSL (now TLS) to connect to the server.  For this to work
-    #         OpenSSL [OSSL] and the Ruby OpenSSL [RSSL] extensions need to
-    #         be installed.
+    #         to use SSL (now TLS) to connect to the server.
     #         If +options[:ssl]+ is a hash, it's passed to
     #         OpenSSL::SSL::SSLContext#set_params as parameters.
     # open_timeout:: Seconds to wait until a connection is opened