Inside the Tooltip of your code, remove this line of code.
<td style="padding:0">{point.y}% </td>
This is the code, where the y axis is being populated with the percentage. Once you remove it, or just remove the
{point.y}%
part, it will work and you won't see the percentage again.
This code (I believe) creates the percentage and prints on the screen. So if you want to write it anywhere else, you can use it again to print the value.
However, it is a good approach to read the API of the library, rather than just the existing or provided code by the library developers. In their API they explain the code very well. So before asking a question, atleast try to Google out the question once. 99% problems are already solved.