Remove unused has_properties function

lib/class-wp-theme-json-gutenberg.php

@@ -495,21 +495,6 @@ private static function get_property_value( $styles, $path ) {
 		return $value;
 	}
 
-	/**
-	 * Whether the metadata contains a key named properties.
-	 *
-	 * @param array $metadata Description of the style property.
-	 *
-	 * @return boolean True if properties exists, false otherwise.
-	 */
-	private static function has_properties( $metadata ) {
-		if ( array_key_exists( 'properties', $metadata ) ) {
-			return true;
-		}
-
-		return false;
-	}
-
 	/**
 	 * Given a styles array, it extracts the style properties
 	 * and adds them to the $declarations array following the format: