Because row_drop_table_for_mysql_no_commit() checks with dict_load_table()
if the table was successfully dropped, we cannot pass table->name to it.

row_merge_drop_table(): Pass a copy of table->name to
row_drop_table_for_mysql().

row_prebuilt_free(): Do not dereference prebuilt->table->name after a
successful invocation of row_add_table_to_background_drop_list().  The
table object may be freed at any time.  Remove the debug message
"Dropping table".