That is called draft which is a [feature](https://meta.stackexchange.com/q/1177/260388) that automatically saves your QA text before posting. There is an option called [**discard**](https://meta.stackexchange.com/a/126299/260388) provided to manually clear saved draft.  
 
An image for reference:


[![enter image description here][1]][1]


As you can see "Discard" option beside "Post your question" button. It works as cancelling only.


  [1]: https://i.sstatic.net/gNEuU.png