Media: Reverts get_attached_file() changes for normalized Windows paths.

Based on feedback from network storage configurations there was a noticed slowdown due to the usage of the `path_join()` function. This needs more time to find a workaround.

Follow-up to [53934].
Props mreishus, SergeyBiryukov, desrosj, mikeschroder.
Reverts [53934].
See #56924.


git-svn-id: https://develop.svn.wordpress.org/trunk@54712 602fd350-edb4-49c9-b593-d223f7449a82

src/wp-includes/functions.php

@@ -2079,7 +2079,6 @@ function wp_mkdir_p( $target ) {
  * For example, '/foo/bar', or 'c:\windows'.
  *
  * @since 2.5.0
- * @since 6.1.0 Allows normalized Windows paths (forward slashes).
  *
  * @param string $path File path.
  * @return bool True if path is absolute, false is not absolute.
@@ -2110,11 +2109,6 @@ function path_is_absolute( $path ) {
 		return true;
 	}
 
-	// Normalized Windows paths for local filesystem and network shares (forward slashes).
-	if ( preg_match( '#(^[a-zA-Z]+:/|^//[\w!@\#\$%\^\(\)\-\'{}\.~]{1,15})#', $path ) ) {
-		return true;
-	}
-
 	// A path starting with / or \ is absolute; anything else is relative.
 	return ( '/' === $path[0] || '\\' === $path[0] );
 }