Twenty Seventeen: Revert usage of str_contains() in theme files.

The theme supports WordPress 4.7 or later, while the polyfill for `str_contains()` only exists in WordPress 5.9 or later.

Follow-up to [55988].

Props poena.
See #60241.

git-svn-id: https://develop.svn.wordpress.org/trunk@57275 602fd350-edb4-49c9-b593-d223f7449a82

src/wp-content/themes/twentyseventeen/inc/icon-functions.php

@@ -130,7 +130,7 @@ function twentyseventeen_nav_menu_social_icons( $item_output, $item, $depth, $ar
 	// Change SVG icon inside social links menu if there is supported URL.
 	if ( 'social' === $args->theme_location ) {
 		foreach ( $social_icons as $attr => $value ) {
-			if ( str_contains( $item_output, $attr ) ) {
+			if ( false !== strpos( $item_output, $attr ) ) {
 				$item_output = str_replace( $args->link_after, '</span>' . twentyseventeen_get_svg( array( 'icon' => esc_attr( $value ) ) ), $item_output );
 			}
 		}

src/wp-content/themes/twentyseventeen/template-parts/post/content-audio.php

@@ -46,7 +46,7 @@
 		$audio   = false;
 
 		// Only get audio from the content if a playlist isn't present.
-	if ( ! str_contains( $content, 'wp-playlist-script' ) ) {
+	if ( false === strpos( $content, 'wp-playlist-script' ) ) {
 		$audio = get_media_embedded_in_content( $content, array( 'audio' ) );
 	}
 

src/wp-content/themes/twentyseventeen/template-parts/post/content-video.php

@@ -46,7 +46,7 @@
 		$video   = false;
 
 		// Only get video from the content if a playlist isn't present.
-	if ( ! str_contains( $content, 'wp-playlist-script' ) ) {
+	if ( false === strpos( $content, 'wp-playlist-script' ) ) {
 		$video = get_media_embedded_in_content( $content, array( 'video', 'object', 'embed', 'iframe' ) );
 	}
 	?>