[FIX] web, *: drop o_dropdown_toggler_btnclasses

Drop `o_dropdown_toggler_btn` class in favor of `o_dropdown_toggler`.
o_dropdown_toggler_btn was initially introduced in ~13.3, but it's now
obsolete.

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

@@ -65,6 +65,10 @@
 .o_dropdown {
   @extend .dropdown;
 
+  &_toggler {
+    @extend .dropdown-toggle;
+  }
+
   &_menu {
     @extend .dropdown-menu;
 
@@ -94,7 +98,7 @@
   cursor: pointer;
 }
 
-button.o_dropdown_toggler, button.o_dropdown_toggler_btn {
+button.o_dropdown_toggler {
   > span {
     min-width: max-content;
   }

addons/web/static/src/legacy/js/views/graph/graph_controller.js

@@ -193,7 +193,7 @@ var GraphController = AbstractController.extend({
             this.groupByMenu.el.classList.add('o_group_by_menu');
         }
         // Update button classes accordingly to the current mode
-        const buttons = actionsContainer.querySelectorAll('.o_dropdown_toggler_btn');
+        const buttons = actionsContainer.querySelectorAll('.o_dropdown_toggler');
         for (const button of buttons) {
             button.classList.remove('btn-secondary');
             if (this.isEmbedded) {

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

@@ -59,7 +59,7 @@
                 top: 5px;
                 right: 10px;
             }
-            .o_dropdown_toggler_btn {
+            .o_dropdown_toggler {
                 margin-right: 15px;
             }
         }

addons/web/static/src/legacy/xml/base.xml

@@ -153,7 +153,7 @@
 <t t-name="web.DropdownMenu" owl="1">
     <div class="btn-group o_dropdown" t-att-class="{ show: state.open }">
         <button type="button"
-            class="o_dropdown_toggler_btn btn btn-secondary"
+            class="o_dropdown_toggler btn btn-secondary"
             t-attf-class="{{ icon || displayCaret || displayChevron ? 'd-flex align-items-center ' : ''}} {{ displayCaret || displayChevron ? 'pr-1 ' : ''}}"
             t-att-aria-expanded="state.open ? 'true' : 'false'"
             tabindex="-1"