fix: move account deletion email to dotdigital

[evemartin]

Dotdigital template: https://r1-app.dotdigital.com/Campaigns/Step/EasyEditor.aspx?id=1567477

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This change is 

[faucomte97]

Reviewed 5 of 7 files at r1, 2 of 2 files at r2, all commit messages.
Reviewable status: all files reviewed, 2 unresolved discussions (waiting on @evemartin)

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cfl_common/common/mail.py line 14 at r2 (raw file):

    "admin_given": 1569057,
    "admin_revoked": 1569071,
    "delete_account": 1567477,

Twice? 🤔

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portal/tests/test_teacher.py line 856 at r2 (raw file):

        page = HomePage(self.selenium).go_to_teacher_login_page().login_failure(email, password)

        assert page.has_login_failed("form-login-teacher", INVALID_LOGIN_MESSAGE)

You can bring this back now

Code quote:

        page = page.open_account_tab()

        # test actual deletion
        page.browser.find_element(By.ID, "id_delete_password").send_keys(password)
        page.browser.find_element(By.ID, "delete_account_button").click()

        time.sleep(FADE_TIME)
        page.browser.find_element(By.ID, "delete_button").click()

        # back to homepage
        assert page.browser.find_element(By.CLASS_NAME, "banner--homepage")

        # user should not be able to login now
        page = HomePage(self.selenium).go_to_teacher_login_page().login_failure(email, password)

        assert page.has_login_failed("form-login-teacher", INVALID_LOGIN_MESSAGE)

[faucomte97]

Reviewed 2 of 2 files at r3, all commit messages.
Reviewable status: complete! all files reviewed, all discussions resolved (waiting on @evemartin)