allow overriding default disabled filetypes

The check for 'filetype' in the internal_filetypes map has been removed
from the is_ft_disabled function. This change allows users to override
default disabled filetypes.

Author: manshengyang

lua/copilot/client/filetypes.lua

@@ -69,11 +69,6 @@ function M.is_ft_disabled(ft, filetypes)
       string.format("'filetype' %s rejected by config filetypes[%s]", ft, "*")
   end
 
-  if M.internal_filetypes[short_ft] ~= nil then
-    return not M.internal_filetypes[short_ft],
-      string.format("'filetype' %s rejected by internal_filetypes[%s]", ft, short_ft)
-  end
-
   return false
 end