Comments: Make `wp_update_comment()` return a `WP_Error` object for a canceled...

Comments: Make `wp_update_comment()` return a `WP_Error` object for a canceled update, if `$wp_error` parameter is true.

Remove redundant checks for `wp_update_comment()` results being `false`, as the function always returns a `WP_Error` object now if `$wp_error` is true.

Follow-up to [48154], [48215], [48216].

See #39732.
Built from https://develop.svn.wordpress.org/trunk@48218


git-svn-id: https://core.svn.wordpress.org/trunk@47987 1a063a9b-81f0-0310-95a4-ce76da25c4cd