fix(setup): group override defaults link to ''

[EdenEast]

Instead of having to know that the highlight group you are overriding is
is linked and setting link = '' this is done automatically for you.

[mehalter]

Ever since this PR was merged, none of my custom highlight groups work so for now I have pinned my plugin to using the commit before this. Is this considered a breaking change that I need to do something to fix in my user configuration? Here is my user configuration that is not working at all anymore:

{
  options = {
    dim_inactive = true,
    styles = { comments = "italic" },
  },
  specs = {
    all = {
      telescope = {
        bg_alt = "bg2",
        bg = "bg1",
        fg = "fg1",
        green = "green",
        red = "red",
      },
    },
  },
  groups = {
    all = {
      WinBar = { fg = "fg2", bg = "bg1" },
      WinBarNC = { fg = "fg3", bg = "bg0" },
      HighlightURL = { style = "underline" },
      MiniIndentscopeSymbol = { link = "PreProc" },
      NormalFloat = { link = "Normal" },
      TelescopeBorder = { fg = "telescope.bg_alt", bg = "telescope.bg" },
      TelescopeNormal = { bg = "telescope.bg" },
      TelescopePreviewBorder = { fg = "telescope.bg", bg = "telescope.bg" },
      TelescopePreviewTitle = { fg = "telescope.bg", bg = "telescope.green" },
      TelescopePromptBorder = { fg = "telescope.bg_alt", bg = "telescope.bg_alt" },
      TelescopePromptNormal = { fg = "telescope.fg", bg = "telescope.bg_alt" },
      TelescopePromptPrefix = { fg = "telescope.red", bg = "telescope.bg_alt" },
      TelescopePromptTitle = { fg = "telescope.bg", bg = "telescope.red" },
      TelescopeResultsBorder = { fg = "telescope.bg", bg = "telescope.bg" },
      TelescopeResultsTitle = { fg = "telescope.bg", bg = "telescope.bg" },
    },
  },
}

[gegoune]

Might be what I am observing as well, discussed briefly in #152 (comment).

[EdenEast]

I was able to find that the compiler was not checking if link was empty like the highlight function. I have a PR: #161 that addresses this. Thanks for pointing this out.