Shortening "mode"

Second attempt to get rid of "too simple" ;-)
* `loose` is the default!! (see https://symfony.com/doc/current/reference/configuration/framework.html#email-validation-mode) So you can't say that it's "too simple".  In other words: "Look guys, we have something here, and we know that it's bullshit. But never mind - this is what we give you out of the box..."
* Maybe it actually is enough for some users?

Author: ThomasLandauer

reference/constraints/Email.rst

@@ -130,17 +130,17 @@ Parameter        Description
 
 **type**: ``string`` **default**: (see below)
 
-This option is optional and defines the pattern used to validate the email
+This option defines the pattern used to validate the email
 address. Valid values are:
 
-* ``loose``, it uses a simple regular expression to validate the address (it
+* ``loose`` uses a simple regular expression (just
   checks that at least one ``@`` character is present, etc.). This validation is
-  too simple and it's recommended to use one of the other modes instead;
-* ``html5``, it validates email addresses using the same regular expression
+  very simple and it's recommended to use one of the other modes instead;
+* ``html5`` uses the same regular expression
   as the `HTML5 email input element`_, making the backend validation consistent
   with the one provided by browsers;
-* ``strict``, it uses the `egulias/email-validator`_ library (which you must
-  install separately) to validate the addresses according to the `RFC 5322`_.
+* ``strict`` uses the `egulias/email-validator`_ library (which you must
+  install separately) to validate according to `RFC 5322`_.
 
 The default value used by this option is set in the
 :ref:`framework.validation.email_validation_mode <reference-validation-email_validation_mode>`