Replace `NvimWebDeviconsHiTest` command with `checkhealth`


### Discussed in https://github.com/nvim-tree/nvim-web-devicons/discussions/552

<div type='discussions-op-text'>

<sup>Originally posted by **gegoune** January 26, 2025</sup>
@alex-courtis what do you think about replacing `NvimWebDeviconsHiTest` to `:checkhealth nvim-web-devicons`? Can keep the same output but will get whatever benefits `:che` gives us for free.</div>