Turn off unicode filtering by default for non-Windows platforms (UTF-8 consoles)

This is a followup to support for unicode added in rapid7#4950

Author: HD Moore

lib/msf/base/sessions/meterpreter_options.rb

@@ -15,7 +15,7 @@ def initialize(info = {})
         OptString.new('InitialAutoRunScript', [false, "An initial script to run on session creation (before AutoRunScript)", '']),
         OptString.new('AutoRunScript', [false, "A script to run automatically on session creation.", '']),
         OptBool.new('AutoSystemInfo', [true, "Automatically capture system information on initialization.", true]),
-        OptBool.new('EnableUnicodeEncoding', [true, "Automatically encode UTF-8 strings as hexadecimal", true]),
+        OptBool.new('EnableUnicodeEncoding', [true, "Automatically encode UTF-8 strings as hexadecimal", Rex::Compat.is_windows]),
         OptPath.new('HandlerSSLCert', [false, "Path to a SSL certificate in unified PEM format, ignored for HTTP transports"])
       ], self.class)
   end