cleanup: remove convert_dash_to_underscore

it was a no-op, plugin variables don't have dashes

include/my_getopt.h

@@ -134,15 +134,6 @@ double getopt_double_limit_value(double num, const struct my_option *optp,
 ulonglong getopt_double2ulonglong(double);
 double getopt_ulonglong2double(ulonglong);
 
-static inline void convert_dash_to_underscore(char *str, size_t len)
-{
-  for (char *p= str; p <= str+len; p++)
-    if (*p == '-')
-      *p= '_';
-    else if (*p != '_' && isalnum(*p) == 0)
-      break;
-}
-
 static inline void convert_underscore_to_dash(char *str, size_t len)
 {
   for (char *p= str; p <= str+len; p++)

sql/sql_plugin.cc

@@ -4220,10 +4220,9 @@ static int test_plugin_options(MEM_ROOT *tmp_root, struct st_plugin_int *tmp,
           var= NULL;
           len= tmp->name.length + strlen(o->name) + 2;
           varname= (char*) alloc_root(mem_root, len);
-          strxmov(varname, tmp->name.str, "-", o->name, NullS);
+          strxmov(varname, tmp->name.str, "_", o->name, NullS);
           // Ok to use latin1, as the variable name is pure ASCII
           my_casedn_str_latin1(varname);
-          convert_dash_to_underscore(varname, len-1);
         }
         if (o->flags & PLUGIN_VAR_NOSYSVAR)
         {