Those things are called 'spinners'.
More accurate info you find by using your friend Google with the search string: CSS: Hide spinners
But to my knowledge, spinners are pretty hard linked to the browser. Dont think you can hide them with a simple CSS code. Until someone proves me wrong, which would be (again) a nice thing.
In the mean time, here is a simple way to restrict the input to numbers.
https://www.dropbox.com/s/c0ohwtlco7zbi ... .capx?dl=0