docs: install guide: remove last bits of API key

The install guide doesn't use GBP API keys as it's considered an
"advanced" feature for now.

docs/how-to-install.md

@@ -244,31 +244,6 @@ systemctl enable --now rabbitmq gentoo-build-publisher-wsgi gentoo-build-publish
 Let's go back to Jenkins.
 
 
-### Create an api key
-
-Executing changes against the GraphQL backend requires an API key.  Let's
-create an API key for the local instance.
-
-```sh
-gbp apikey create gbp
-```
-
-This will generate and print an API key for the user `gbp`.  Copy the API key.
-Now create the file `~/.config/gbpcli.toml`
-
-
-```toml
-[gbpcli]
-url = "http://localhost/"
-auth = { user = "gbp", api_key = "your_API_key" }
-```
-
-Replace `your_API_key` with the API key that was generated above.
-
-You should generate an API key for each system you plan to use the CLI to make
-changes from.  Changes include adding repos and machines, creating tags,
-scheduling builds, etc.
-
 ### Create a job for the Gentoo repo
 
 Tell Gentoo Build Publisher to create a ebuild repo job from the official