If your plugin creates a new table on installation to store its data, you must drop that table when plugin is uninstalled because when plugin is not working, that table is not required at all. Here is how you can do it.
Create new php file in your plugin folder and name it uninstall_plugin_name.php
Add follow code into that file.
'DROP TABLE '.tbl("plugin_table_name ").''
Now uninstall your plugin and you won’t see that table in Database anymore. Have fun.
How To Create New Table On Plugin Installation