[IMP] theme_*: review s_cover templates

This commit aims to review all the occurrences of the `s_cover`
snippet across the themes in order to fix broken selectors.

task-3665300

Part-of: odoo/design-themes#827
Related: odoo/odoo#172725
Signed-off-by: Benoit Socias (bso) <bso@odoo.com>

theme_kea/views/snippets/s_cover.xml

@@ -25,7 +25,7 @@
     </xpath>
     <!-- Button -->
     <xpath expr="//a[hasclass('btn')]" position="replace">
-        <a href="#0" class="btn btn-lg btn-primary">Discover more</a>
+        <a href="#0" class="btn btn-primary">Discover more</a>
     </xpath>
 </template>