Networks and Sites: Officially remove global terms.

Global terms was a feature from the WordPress MU days where multisite and single site installs used different code bases.

In WordPress 3.0, WordPress MU was merged into one location and the UI [14854] and “on” switch [14880] for global terms were completely removed.

Even before this merge, global terms was bug infested and unreliable. After [14854]/[14880], the feature was no longer maintained and became increasingly broken as taxonomies progressed without it (term splitting and term meta do not work at all). At this point, the feature has not worked in 12+ years and there’s no hope for saving it.

This deprecates the remaining global terms related code and no-ops the functions.

Global terms, you don’t have to go home, but you can’t stay here.

Props scribu, wonderboymusic, SergeyBiryukov, nacin, pento, desrosj, johnjamesjacoby, johnbillion, dd32.
Fixes #21734.

git-svn-id: https://develop.svn.wordpress.org/trunk@54240 602fd350-edb4-49c9-b593-d223f7449a82

src/wp-includes/ms-deprecated.php

@@ -730,3 +730,34 @@ function update_user_status( $id, $pref, $value, $deprecated = null ) {
 
 	return $value;
 }
+/**
+ * Determines whether global terms are enabled.
+ *
+ * @since 3.0.0
+ * @since 6.1.0 This function now always returns false.
+ * @deprecated 6.1.0
+ *
+ * @return bool Always returns false.
+ */
+function global_terms_enabled() {
+	_deprecated_function( __FUNCTION__, '6.1.0' );
+
+	return false;
+}
+
+/**
+ * Maintains a canonical list of terms by syncing terms created for each blog with the global terms table.
+ *
+ * @since 3.0.0
+ * @since 6.1.0 This function no longer does anything.
+ * @deprecated 6.1.0
+ *
+ * @param int    $term_id    An ID for a term on the current blog.
+ * @param string $deprecated Not used.
+ * @return int An ID from the global terms table mapped from $term_id.
+ */
+function global_terms( $term_id, $deprecated = '' ) {
+	_deprecated_function( __FUNCTION__, '6.1.0' );
+
+	return $term_id;
+}