refactor(shell)!: remove deprecated open API (#3604)

* refactor(shell)!: remove deprecated open API

`open` has been deprecated since 2.1.0 in favor of tauri-plugin-opener.
This removes:

- the `open` command and its `allow-open`/`deny-open` permissions
  (`shell:default` now grants nothing)
- the `plugins > shell > open` configuration; `init()` returns
  `TauriPlugin<R>` again
- `Shell::open`, the `tauri_plugin_shell::open` module and
  `Error::UnknownProgramName`
- the `open` JavaScript function
- the Android and iOS plugins, since `open` was their only command

* chore(examples): drop the now empty shell:default permission set

---------

Co-authored-by: Lucas Nogueira <lucas@crabnebula.dev>

examples/api/src-tauri/capabilities/base.json

@@ -48,7 +48,6 @@
         }
       ]
     },
-    "shell:default",
     "shell:allow-kill",
     "shell:allow-stdin-write",
     "process:allow-exit",

examples/api/src-tauri/tauri.conf.json

@@ -72,9 +72,6 @@
         }
       }
     },
-    "shell": {
-      "open": true
-    },
     "updater": {
       "pubkey": "dW50cnVzdGVkIGNvbW1lbnQ6IG1pbmlzaWduIHB1YmxpYyBrZXk6IDE5QzMxNjYwNTM5OEUwNTgKUldSWTRKaFRZQmJER1h4d1ZMYVA3dnluSjdpN2RmMldJR09hUFFlZDY0SlFqckkvRUJhZDJVZXAK",
       "dangerousInsecureTransportProtocol": true,