Minor bootstrap 4 fixes:

- Removed 'collapse in' css from wizard as we have 'collapse show' in Bootstrap-4
- Fixed 'Select/Unselect All' button layout for Select2 control used in pgAgent.

web/pgadmin/browser/static/css/wizard.css

@@ -126,7 +126,3 @@ div.wizard-header.wizard-badge > div > div.col-sm-2 > button.ajs-maximized.ajs-m
   margin-top: 20px !important;
   margin-bottom: 10px !important;
 }
-
-.wizard-right-panel_content .collapse.in {
-  display: block;
-}

web/pgadmin/browser/static/js/node.ui.js

@@ -21,7 +21,7 @@ define([
       let $rendered = decorated.call(this);
 
       let $selectAll = $([
-        '<button class="btn btn-xs btn-default" type="button"',
+        '<button class="btn btn-default btn-sm" type="button"',
         ' style="width: 49%;margin: 0 0.5%;">',
         '<i class="fa fa-check-square-o"></i>',
         '<span style="padding: 0px 5px;">',
@@ -30,7 +30,7 @@ define([
       ].join(''));
 
       let $unselectAll = $([
-        '<button class="btn btn-xs btn-default" type="button"',
+        '<button class="btn btn-default btn-sm" type="button"',
         ' style="width: 49%;margin: 0 0.5%;">',
         '<i class="fa fa-square-o"></i><span style="padding: 0px 5px;">',
         gettext('Unselect All'),