AMP: fix linting issues introduced in D38340

Summary:
The file is synced with Jetpack, and D38340 cannot be merged into Jetpack as is as it introduces changes that will not pass our pre-commit hook.
This diff fixes all PHPCS warnings.
Test Plan: * Not much to test here, this only impacts documentation / comments.
Reviewers: goldsounds
Tags: #touches_jetpack_files

Differential Revision: D39590

This commit syncs r r203555-wpcom.

3rd-party/class.jetpack-amp-support.php

@@ -41,7 +41,7 @@ public static function init() {
 		// Post rendering changes for legacy AMP.
 		add_action( 'pre_amp_render_post', array( 'Jetpack_AMP_Support', 'amp_disable_the_content_filters' ) );
 
-		// Transitional mode AMP should not have comment likes
+		// Transitional mode AMP should not have comment likes.
 		add_action( 'the_content', array( 'Jetpack_AMP_Support', 'disable_comment_likes_before_the_content' ) );
 
 		// Add post template metadata for legacy AMP.
@@ -53,15 +53,25 @@ public static function init() {
 		// Sync the amp-options.
 		add_filter( 'jetpack_options_whitelist', array( 'Jetpack_AMP_Support', 'filter_jetpack_options_whitelist' ) );
 
-		// Show admin bar
+		// Show admin bar.
 		add_filter( 'show_admin_bar', array( 'Jetpack_AMP_Support', 'show_admin_bar' ) );
 		add_filter( 'jetpack_comment_likes_enabled', array( 'Jetpack_AMP_Support', 'comment_likes_enabled' ) );
 	}
 
+	/**
+	 * Disable the admin bar on AMP views.
+	 *
+	 * @param Whether bool $show the admin bar should be shown. Default false.
+	 */
 	public static function show_admin_bar( $show ) {
 		return $show && ! self::is_amp_request();
 	}
 
+	/**
+	 * Disable the Comment Likes feature on AMP views.
+	 *
+	 * @param bool $enabled Should comment likes be enabled.
+	 */
 	public static function comment_likes_enabled( $enabled ) {
 		return $enabled && ! self::is_amp_request();
 	}
@@ -116,6 +126,11 @@ public static function amp_disable_the_content_filters() {
 		remove_filter( 'pre_kses', array( 'Filter_Embedded_HTML_Objects', 'maybe_create_links' ), 100 );
 	}
 
+	/**
+	 * Do not add comment likes on AMP requests.
+	 *
+	 * @param string $content Post content.
+	 */
 	public static function disable_comment_likes_before_the_content( $content ) {
 		if ( self::is_amp_request() ) {
 			remove_filter( 'comment_text', 'comment_like_button', 12, 2 );