[IMP] web: remove unused .o_inline_dropdown class

task-3439226

Part-of: odoo#133289

addons/web/static/src/legacy/scss/dropdown.scss

@@ -63,21 +63,6 @@
 }
 
 // = Legacy submenus
-// Workaround appling owl 'vertical nested menu' design.
-// Should be removed once we'll support the 'horizontal' design.
-// ----------------------------------------------------------------------------
-.o_inline_dropdown {
-    .dropdown-menu, .o-dropdown-menu {
-        position: relative;
-        border: 0;
-        padding-top: 0;
-        box-shadow: none;
-
-        > .dropdown-item {
-            padding-left: $dropdown-item-padding-x * 1.5;
-        }
-    }
-}
 
 // TODO probably remove those next rules that target dropdown main classes once
 // the backend searchbar has been refactored to use OWL dropdown components and