Mobile Apps: completely remove the edit post link when in app

Fixes wordpress-mobile/WordPress-iOS#13314

This issue was introduced in #12867.

The original goal of this change was to to hide the Edit Post link
whenever you would access your site via the mobile app's in-app browser.

To hide the Edit Post link, we originally opted to hook into the edit_post_link filter.
While this works, it only changes the string returned for the Edit Post link itself.
It does not account for any "before" or "after" parameters that may be passed
when calling the edit_post_link function; those are not part of the filter:
https://github.com/WordPress/WordPress/blob/001ffe81fbec4438a9f594f330e18103d21fbcd7/wp-includes/link-template.php#L1439

Instead, let's shortcircuit that link earlier, by hooking into the get_edit_post_link filter.
If that filter is set to return an empty string, the edit_post_link function will return early:
https://github.com/WordPress/WordPress/blob/001ffe81fbec4438a9f594f330e18103d21fbcd7/wp-includes/link-template.php#L1420

class.jetpack.php

@@ -641,7 +641,7 @@ function( $callable ) {
 
 		// Hide edit post link if mobile app.
 		if ( Jetpack_User_Agent_Info::is_mobile_app() ) {
-			add_filter( 'edit_post_link', '__return_empty_string' );
+			add_filter( 'get_edit_post_link', '__return_empty_string' );
 		}
 
 		// Update the Jetpack plan from API on heartbeats