chore: remove unmaintained examples (#4317)

Remove unmainted examples. All examples are part of the multi-runner
setup.

Author: npalm

.github/workflows/terraform.yml

@@ -132,12 +132,9 @@ jobs:
         example:
           [
             "default",
-            "ubuntu",
             "prebuilt",
-            "arm64",
             "ephemeral",
             "termination-watcher",
-            "windows",
             "multi-runner",
           ]
     defaults:

docs/examples/index.md

@@ -3,9 +3,9 @@
 Examples are located in the [examples](https://github.com/philips-labs/terraform-aws-github-runner/tree/main/examples) directory. The following examples are provided:
 
 - _[Default](default.md)_: The default example of the module
-- _[ARM64](arm64.md)_: Example usage with ARM64 architecture
 - _[Ephemeral](ephemeral.md)_: Example usages of ephemeral runners based on the default example.
-- _[Multi Runner](multi-runner.md)_ : Example usage of creating a multi runner which creates multiple runners/ configurations with a single deployment
+- _[Multi Runner](multi-runner.md)_ : Example usage of creating a multi runner which creates multiple runners/ configurations with a single deployment. The examples including: "arm64", "windows", and "ubuntu" runners.
 - _[Permissions boundary](permissions-boundary.md)_: Example usages of permissions boundaries.
 - _[Prebuilt Images](prebuilt.md)_: Example usages of deploying runners with a custom prebuilt image.
 - _[Windows](windows.md)_: Example usage of creating a runner using Windows as the OS.
+- _[Termination watcher](termination-watcher.md)_: Example usages of termination watcher.