[FIX] web_editor: typography adaptations

Prior of this commit the paragraph margin-bottom was forced to '0'
braking the typography's vertical rhythm.

This commit will remove the customisation rules restoring bootstrap
default values for the backend.

task-2798759

closes odoo/odoo#86740

Signed-off-by: Antoine Guenet <age@odoo.com>

addons/web_editor/static/src/scss/web_editor.backend.scss

@@ -14,15 +14,8 @@
         font-family: inherit !important;
         line-height: inherit !important;
         color: inherit !important;
+    }
 
-        p, div {
-            font-family: 'Lucida Grande', Helvetica, Verdana, Arial, sans-serif;
-            font-size: 13px;
-        }
-    }
-    ul > li > p, p {
-        margin: 0px;
-    }
     > iframe {
         display: block;
         width: 100%;