Revert "tests/modules-performance: add nvim-cmp to extraPlugins when necessary"

This reverts commit bb5b0a2.

This change defeats the purpose of the dependency test. Revert it.
The test should verify that dependencies are correctly pulled. If
upstream plugin doesn't have dependency anymore, then a suitable
alternative should be used, not dependencies added manually.

Author: stasjok

tests/test-sources/modules/performance/combine-plugins.nix

@@ -64,8 +64,6 @@ in
       extraPlugins = with pkgs.vimPlugins; [
         # Depends on nvim-cmp
         cmp-dictionary
-        # We have to manually add cmp-dictionary's dependence: nvim-cmp
-        nvim-cmp
         # Depends on telescope-nvim which itself depends on plenary-nvim
         telescope-undo-nvim
       ];
@@ -334,8 +332,6 @@ in
         telescope-nvim
         # Only its dependency (nvim-cmp) won't be combined, but not the plugin itself
         cmp-dictionary
-        # We have to manually add cmp-dictionary's dependence: nvim-cmp
-        nvim-cmp
         # More plugins
         gitsigns-nvim
         luasnip