Revert "fix: clear highlights before applying theme"

This reverts commit dc7c6dc, which may
have caused plugin highlight related issues, as mentioned in #223 and #224.
I've identified that reverting this commit resolves these issues.

lua/github-theme/init.lua

@@ -12,7 +12,6 @@ init.setup = function(user_config)
   end
 
   -- Load colorscheme
-  vim.cmd([[hi clear]]) -- necessary to clear highlight from previous theme, otherwise it will be layered on top of the new one
   util.load(theme.setup(config.schema))
 end