remove registers.nvim

Which-key.nvim can show register content too, with much more features.
I found this info on https://toroid.org/modern-neovim.

lua/config/registers-nvim.lua

@@ -1,11 +0,0 @@
--- do not show empty registers
-vim.g.registers_show_empty_registers = 0
-
--- register popup window border style
-vim.g.registers_window_border = 'rounded'
-
--- register popup window width
-vim.g.registers_window_max_width = 80
-
--- hide registers filled only with whitespace
-vim.g.registers_hide_only_whitespace = 1