Code Modernization: Remove `-webkit-appearance` CSS declarations.

This changeset removes the deprecated `-webkit-appearance` CSS property used in `customizer-controls.css`. It doesn't change anything to the interface.

Props laurent22777, desrosj, celloexpressions, costdev, rolfsiebers, audrasjb, Clorith.
Fixes #38431.

Built from https://develop.svn.wordpress.org/trunk@54188


git-svn-id: http://core.svn.wordpress.org/trunk@53747 1a063a9b-81f0-0310-95a4-ce76da25c4cd

wp-admin/css/customize-controls-rtl.css

@@ -473,7 +473,6 @@ body.trashing #publish-settings {
 	height: 20px;
 	cursor: pointer;
 	box-shadow: none;
-	-webkit-appearance: none;
 	background: transparent;
 	color: #50575e;
 	border: none;

wp-admin/css/customize-controls.css

@@ -472,7 +472,6 @@ body.trashing #publish-settings {
 	height: 20px;
 	cursor: pointer;
 	box-shadow: none;
-	-webkit-appearance: none;
 	background: transparent;
 	color: #50575e;
 	border: none;

wp-includes/version.php

@@ -16,7 +16,7 @@
  *
  * @global string $wp_version
  */
-$wp_version = '6.1-alpha-54187';
+$wp_version = '6.1-alpha-54188';
 
 /**
  * Holds the WordPress DB revision, increments when changes are made to the WordPress DB schema.