Add back UTF8_GENERAL50_CI

Author: testn

lib/constants/charsets.js

@@ -223,6 +223,7 @@ exports.UTF8MB4_VIETNAMESE_CI = 247;
 exports.GB18030_CHINESE_CI = 248;
 exports.GB18030_BIN = 249;
 exports.GB18030_UNICODE_520_CI = 250;
+exports.UTF8_GENERAL50_CI = 253; // deprecated
 exports.UTF8MB4_0900_AI_CI = 255;
 exports.UTF8MB4_DE_PB_0900_AI_CI = 256;
 exports.UTF8MB4_IS_0900_AI_CI = 257;