I18N: Remove unnecessary HTML from "Active:" strings in wp-admin/themes.php.

Follow-up to [45435].

Props ramiy.
Fixes #49243.
Built from https://develop.svn.wordpress.org/trunk@47090


git-svn-id: http://core.svn.wordpress.org/trunk@46890 1a063a9b-81f0-0310-95a4-ce76da25c4cd

wp-includes/customize/class-wp-customize-theme-control.php

@@ -110,7 +110,7 @@ class WP_Customize_Theme_Control extends WP_Customize_Control {
 			<# if ( data.theme.active ) { #>
 				<div class="theme-id-container">
 					<h3 class="theme-name" id="{{ data.section }}-{{ data.theme.id }}-name">
-						<span><?php _e( 'Previewing:' ); ?></span> {{ data.theme.name }}
+						<span><?php _ex( 'Previewing:', 'theme' ); ?></span> {{ data.theme.name }}
 					</h3>
 					<div class="theme-actions">
 						<button type="button" class="button button-primary customize-theme" aria-label="<?php echo esc_attr( $customize_label ); ?>"><?php _e( 'Customize' ); ?></button>