Reduce email and realname columns to 191 chars

The varchar(255) implemented to address issue #8017 was causing issues
with utf8mb4 encoding due a limitation in the size of indexes in MySQL.

Fixes #20465

admin/schema.php

@@ -828,17 +828,16 @@
 $g_upgrade[194] = array( 'UpdateFunction', 'check_token_serialization', array() );
 $g_upgrade[195] = array( 'UpdateFunction', 'stored_filter_migrate', array() );
 
-# Step 196 used to increase length of user.username column to 255 chars.
-# This was causing issues with utf8mb4 charset on MySQL / InnoDB engine;
-# the column will be reduced to 191 chars (see upgrade step 206 below).
+# Steps 196, 197 and 199 used to increase length of user.username, user.realname
+# and user.email columns to 255 chars. This causes issues with utf8mb4 charset
+# on MySQL when using the InnoDB engine due to a limitation on index key size
+# to 767 bytes.
+# The columns will be reduced to 191 chars (see upgrade steps 206-208 below).
 $g_upgrade[196] = null;
-
-$g_upgrade[197] = array( 'AlterColumnSQL', array( db_get_table( 'user' ), "
-	realname				C(255)	$t_notnull DEFAULT \" '' \"" ) );
+$g_upgrade[197] = null;
 $g_upgrade[198] = array( 'AlterColumnSQL', array( db_get_table( 'user' ), "
 	password				C(64)	$t_notnull DEFAULT \" '' \"" ) );
-$g_upgrade[199] = array( 'AlterColumnSQL', array( db_get_table( 'user' ), "
-	email					C(255)	$t_notnull DEFAULT \" '' \"" ) );
+$g_upgrade[199] = null;
 
 # Release marker: 1.3.0-beta.1 - 1.3.0-beta.3
 
@@ -869,8 +868,13 @@
 # Enable gravatar plugin if avatars are enabled
 $g_upgrade[205] = array( 'UpdateFunction', 'gravatar_plugin', array() );
 
+# Limiting column size, planning for future MySQL utf8mb4 support (see #20465)
 $g_upgrade[206] = array( 'AlterColumnSQL', array( db_get_table( 'user' ), "
 	username				C(191)	$t_notnull DEFAULT \" '' \"" ) );
+$g_upgrade[207] = array( 'AlterColumnSQL', array( db_get_table( 'user' ), "
+	realname				C(191)	$t_notnull DEFAULT \" '' \"" ) );
+$g_upgrade[208] = array( 'AlterColumnSQL', array( db_get_table( 'user' ), "
+	email					C(191)	$t_notnull DEFAULT \" '' \"" ) );
 
 # Release marker: 1.3.0