Remove uvx shell completion instructions (#7459)

## Summary

I misunderstood and this isn't necessary.

docs/getting-started/installation.md

@@ -181,25 +181,6 @@ To enable shell autocompletion for uv commands, run one of the following:
 
 Then restart the shell or source the shell config file.
 
-You can also enable shell autocompletion for uvx by running the same commands, replacing `uv` with
-`uvx`:
-
-=== "Linux and macOS"
-
-    ```bash
-    # Determine your shell (e.g., with `echo $SHELL`), then run one of:
-    echo 'eval "$(uvx generate-shell-completion bash)"' >> ~/.bashrc
-    echo 'eval "$(uvx generate-shell-completion zsh)"' >> ~/.zshrc
-    echo 'uvx generate-shell-completion fish | source' >> ~/.config/fish/config.fish
-    echo 'eval (uvx generate-shell-completion elvish | slurp)' >> ~/.elvish/rc.elv
-    ```
-
-=== "Windows"
-
-    ```powershell
-    Add-Content -Path $PROFILE -Value '(& uvx generate-shell-completion powershell) | Out-String | Invoke-Expression'
-    ```
-
 ## Uninstallation
 
 If you need to remove uv from your system, just remove the `uv` and `uvx` binaries: