[FIX] website: remove footer top border

The footer of Odoo is composed of 3 main elements: a <footer/> with a
.oe_structure and the footer copyright inside. The footer had a
transparent top border which was there for technical reason: making sure
the .oe_structure content was "1px" below the end-of-page content so
that dropping a snippet at the end of page but also in the footer was
possible (otherwise the dropzones would be at the exact same position).

This border which was invisible at the time may now become visible in
more cases so we have to remove it. Another hacky solution is made to
replace the old one, while remembering the footer usability is being
reviewed anyway.

Related to task-2197038

closes odoo/odoo#51997

Signed-off-by: Quentin Smetz (qsm) <qsm@odoo.com>

addons/website/static/src/scss/website.edit_mode.scss

@@ -65,6 +65,13 @@ $-editor-messages-margin-x: 2%;
 .editor_enable [data-oe-readonly]:hover {
     cursor: default;
 }
+.oe_structure_solo > .oe_drop_zone {
+    // TODO implement something more robust. This is currently for our only
+    // use case of oe_structure_solo: the footer. The dropzone in there need to
+    // be 1px lower that the end-of-page dropzone to distinguish them. The
+    // usability has to be reviewed anyway.
+    transform: translateY(10px); // For some reason "1px" is not enough...
+}
 
 /* Prevent the text contents of draggable elements from being selectable. */
 [draggable] {

addons/website/static/src/scss/website.scss

@@ -144,12 +144,6 @@ $-header-nav-link-height: $nav-link-height;
     @if color('footer') {
         @include o-bg-color(color('footer'));
     }
-
-    > #footer {
-        // FIXME needed to prevent the dropzone at the bottom of the #wrap element
-        // to be at the same place of the dropzone at the top of the #footer element
-        border-top: 1px solid transparent;
-    }
 }
 h2, h3, h4, h5, h6 {
     color: color('h2');