Formatting: Deprecate wp_slash_strings_only() in favor of wp_slash().

The reason for introducing `wp_slash_strings_only()` in [46454] was to keep non-string values untouched.

Later, `wp_slash()` itself was updated in [48433] to prevent changing non-string values.

To avoid confusion, `wp_slash_strings_only()` is now deprecated.

Props ayeshrajans, ocean90.
Fixes #50635.

git-svn-id: https://develop.svn.wordpress.org/trunk@49188 602fd350-edb4-49c9-b593-d223f7449a82

src/wp-includes/formatting.php

@@ -5545,33 +5545,6 @@ function wp_unslash( $value ) {
 	return stripslashes_deep( $value );
 }
 
-/**
- * Adds slashes to only string values in an array of values.
- *
- * This should be used when preparing data for core APIs that expect slashed data.
- * This should not be used to escape data going directly into an SQL query.
- *
- * @since 5.3.0
- *
- * @param mixed $value Scalar or array of scalars.
- * @return mixed Slashes $value
- */
-function wp_slash_strings_only( $value ) {
-	return map_deep( $value, 'addslashes_strings_only' );
-}
-
-/**
- * Adds slashes only if the provided value is a string.
- *
- * @since 5.3.0
- *
- * @param mixed $value
- * @return mixed
- */
-function addslashes_strings_only( $value ) {
-	return is_string( $value ) ? addslashes( $value ) : $value;
-}
-
 /**
  * Extract and return the first URL from passed content.
  *