Revert "MDEV-14429 sql_safe_updates in my.cnf not work"

This reverts commit dc3a20b191362227a6f85fadfc3a8b6c76f69ec6.

It requires GET_BIT in include/my_getopt.h, which is available
only in 10.3+

mysql-test/r/mysqld--help.result

@@ -790,7 +790,6 @@ The following specify which files/extra groups are read (specified before remain
  this size
  --sql-mode=name     Syntax: sql-mode=mode[,mode[,mode...]]. See the manual
  for the complete list of valid sql modes
- --sql-safe-updates  sql_safe_updates
  --stack-trace       Print a symbolic stack trace on failure
  (Defaults to on; use --skip-stack-trace to disable.)
  --stored-program-cache=# 
@@ -1082,7 +1081,6 @@ slow-launch-time 2
 slow-query-log FALSE
 sort-buffer-size 2097152
 sql-mode 
-sql-safe-updates FALSE
 stack-trace TRUE
 stored-program-cache 256
 symbolic-links FALSE

sql/sys_vars.cc

@@ -2719,7 +2719,7 @@ static Sys_var_bit Sys_auto_is_null(
 
 static Sys_var_bit Sys_safe_updates(
        "sql_safe_updates", "sql_safe_updates",
-       SESSION_VAR(option_bits), CMD_LINE(REQUIRED_ARG), OPTION_SAFE_UPDATES,
+       SESSION_VAR(option_bits), NO_CMD_LINE, OPTION_SAFE_UPDATES,
        DEFAULT(FALSE));
 
 static Sys_var_bit Sys_buffer_results(

sql/sys_vars.h

@@ -1443,6 +1443,7 @@ public:
     bitmask= reverse_semantics ? ~bitmask_arg : bitmask_arg;
     set(global_var_ptr(), def_val);
     SYSVAR_ASSERT(def_val < 2);
+    SYSVAR_ASSERT(getopt.id == -1); // force NO_CMD_LINE
     SYSVAR_ASSERT(size == sizeof(ulonglong));
   }
   bool session_update(THD *thd, set_var *var)