Remove `TC_TO_DSCP_MAP` in `config qos clear` command

[bingwang-ms]

What I did

This PR is to update command config qos clear. Before the update: config qos clear doesn't clear the TC_TO_DSCP_MAP. After the update TC_TO_DSCP_MAP is cleared when running config qos clear. I have confirmed that even if TC_TO_DSCP_MAP doesn't exist, deleting an inexistent table won't cause exception.

How I did it

Update the list QOS_TABLE_NAMES to add TC_TO_DSCP_MAP.

How to verify it

The change is verified on a physical testbed.

Previous command output (if the output of a command-line utility has changed)

New command output (if the output of a command-line utility has changed)