[FIX] theme_*: remove mb-2 class on orphan buttons

*: anelusia, artists, aviato, graphene, kiddo, loftspace, monglia,
notes, odoo_experts, paptic, test_custo, yes

The community PR [125824] introduces an automatic check on buttons to
add the `mb-2` class when several buttons follow each other, so that
they have space to breathe when split on multiple lines.
For consistency, this commit therefore removes most `mb-2` occurrences
on buttons within themes as long as they are alone on their line, but
keeps or adds the class when several buttons are next to each other.

[125824]: https://github.com/odoo/odoo/pull/125824

task-3369604

closes odoo/design-themes#680

Related: odoo/odoo#125824
Signed-off-by: Benjamin Vray (bvr) <bvr@odoo.com>

theme_anelusia/views/snippets/s_color_blocks_2.xml

@@ -50,7 +50,7 @@
             <i class="fa fa-venus-mars fa-5x m-3"/>
             <h2>Fancy for them</h2>
             <p>Are you looking for sustainable clothing for men or women? Discover our exclusive fashion brand for both of you.</p>
-            <a href="#" class="btn btn-primary mb-2 btn-lg">More Details</a>
+            <a href="#" class="btn btn-primary btn-lg">More Details</a>
         </div>
     </xpath>
 </template>

theme_anelusia/views/snippets/s_media_list.xml

@@ -66,7 +66,7 @@
     </xpath>
     <!-- Media #02 - Add a button -->
     <xpath expr="//div[hasclass('s_media_list_item')][2]//p" position="after">
-        <a href="#" class="btn btn-primary mb-2">Read more</a>
+        <a href="#" class="btn btn-primary">Read more</a>
     </xpath>
 
     <!-- Remove Media #03 -->