[FIX] mass_mailing: needlessly large gap in mailing list contacts

Prior to this commit:
In email marketing, when we click on the import button of the "mailing list
contacts", we find a needlessly large gap beneath the contact list.

Post this commit:
The class which creates the space is removed and hence we get the required output.

Task-3258581

closes odoo/odoo#119884

X-original-commit: 1ee98fb9f6bd8289c5ffcada14c3db62afba5a0d
Signed-off-by: Thibault Delavallee (tde) <tde@openerp.com>

addons/mass_mailing/static/src/scss/mass_mailing.scss

@@ -207,11 +207,6 @@
     }
 }
 
-
-.o_mailing_contact_import_list {
-    min-height: 150px;
-}
-
 .o_field_mass_mailing_html {
     display: block;
 

addons/mass_mailing/wizard/mailing_contact_import_views.xml

@@ -15,7 +15,7 @@
                     Each line will be imported as a mailing list contact.
                 </p>
                 <label for="contact_list" class="mb-2">Contact List</label>
-                <field name="contact_list" class="o_mailing_contact_import_list"
+                <field name="contact_list"
                     nolabel="1" default_focus="1"
                     placeholder='"Damien Roberts" &lt;d.roberts@example.com&gt;&#10;"Rick Sanchez" &lt;rick_sanchez@example.com&gt;&#10;victor_hugo@example.com'/>
                 <p class="text-muted mb-0">