Clarify TOTP reset/status logic

The current TOTP reset logic as of GUACAMOLE-770 works well, but feels somewhat clunky in its use of a checkbox to request that TOTP status be cleared. Checkboxes typically represent state, but the TOTP form leverages checkboxes to represent both an action and current state:

Rather than conceptualize things as an action ("reset") and represent that action with a checkbox, it would be better to consistently use checkboxes to represent state. For example: