fix(terminal): partially revert previous mappings (#6770)

## Description
Commit 4efd0e2bea introduced some changes
to terminal mappings. I tested in a new LazyVim installation and
`sidekick.nvim` is not affected by `<C-/>` any more.

The mappings `hide_underscore` and `hide_slash` don't let user to create
new terminals with `2<C-/>`, `3<C-/>` and so on. Instead they hide the
terminal and user can't open split terminals next to each other any
more.

Therefore, I believe it would be a better default to revert these 2
mappings explicitly.

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## Checklist

- [x] I've read the
[CONTRIBUTING](https://github.com/LazyVim/LazyVim/blob/main/CONTRIBUTING.md)
guidelines.

lua/lazyvim/plugins/util.lua

@@ -23,8 +23,6 @@ return {
             nav_j = { "<C-j>", term_nav("j"), desc = "Go to Lower Window", expr = true, mode = "t" },
             nav_k = { "<C-k>", term_nav("k"), desc = "Go to Upper Window", expr = true, mode = "t" },
             nav_l = { "<C-l>", term_nav("l"), desc = "Go to Right Window", expr = true, mode = "t" },
-            hide_slash = { "<C-/>", "hide", desc = "Hide Terminal", mode = { "t", "n" } },
-            hide_underscore = { "<c-_>", "hide", desc = "which_key_ignore", mode = { "t", "n" } },
           },
         },
       },