minor #6246 removed duplicate lines (seferov)

This PR was submitted for the 3.0 branch but it was merged into the 2.3 branch instead (closes #6246).

Discussion
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removed duplicate lines

| Q             | A
| ------------- | ---
| Doc fix?      | yes
| New docs?     | no

The line is already included on the next paragraph.

Commits
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24c7c75 removed duplicate lines

cookbook/email/gmail.rst

@@ -120,9 +120,6 @@ If your application uses ``tls`` encryption or ``oauth`` authentication, you
 must override the default options by defining the ``encryption`` and ``auth_mode``
 parameters.
 
-If you are using 2-Step-Verification, you must `generate an App password`_ and
-use this as your ``mailer_password`` value.
-
 If your Gmail account uses 2-Step-Verification, you must `generate an App password`_
 and use it as the value of the ``mailer_password`` parameter. You must also ensure
 that you `allow less secure apps to access your Gmail account`_.