Coding Standards: Remove redundant check in insert_with_markers().

The check in the `elseif` branch would always be true, as the preceding `if` is for `! $found_marker`.

Follow-up to [34740].

Props justlevine.
See #63268.

git-svn-id: https://develop.svn.wordpress.org/trunk@60480 602fd350-edb4-49c9-b593-d223f7449a82

Author: SergeyBiryukov

src/wp-admin/includes/misc.php

@@ -205,7 +205,7 @@ function insert_with_markers( $filename, $marker, $insertion ) {
 
 		if ( ! $found_marker ) {
 			$pre_lines[] = $line;
-		} elseif ( $found_marker && $found_end_marker ) {
+		} elseif ( $found_end_marker ) {
 			$post_lines[] = $line;
 		} else {
 			$existing_lines[] = $line;