terraform: Extract to zed-extensions/terraform repository (#26475)

This PR extracts the Terraform extension to the
[zed-extensions/terraform](https://github.com/zed-extensions/terraform)
repository.

Release Notes:

- N/A

Cargo.toml

@@ -178,7 +178,6 @@ members = [
     "extensions/ruff",
     "extensions/slash-commands-example",
     "extensions/snippets",
-    "extensions/terraform",
     "extensions/test-extension",
     "extensions/toml",
     "extensions/uiua",