nvim: plugins: Drop conflict-marker

We have been mostly relying on diffconflicts plugin to resolve merge
conflicts. For complex merge conflicts, it becomes difficult to
understand which conflict hunk to pick. The syntax highlighting also
stopped taking effect due to treesitter probably. So just drop this.
Introducing a mapping to jump among conflicts would be helpful.

We let the syntax highlighting entries in our color scheme be, just
in case we decide to revisit this.

nvim/.config/nvim/lua/plugins.lua

@@ -43,7 +43,6 @@ local init = function ()
   }
   use 'tpope/vim-fugitive'
   use 'rhysd/git-messenger.vim'
-  use 'rhysd/conflict-marker.vim'
   use 'salcode/vim-interactive-rebase-reverse'
   use 'whiteinge/diffconflicts'
   use 'sindrets/diffview.nvim'