Remove dependabot from wasmtime (#1713)

Right now we're just getting a lot of noisy "can't parse manifest" error
messages, and with `cargo audit` running on CI we should be alerted to
security vulnerabilities anyway.

.dependabot/config.yml

@@ -1,10 +0,0 @@
-# See https://dependabot.com/docs/config-file/ for a reference.
-version: 1
-update_configs:
-  - package_manager: "rust:cargo"
-    directory: "/"
-    update_schedule: "live"
-    version_requirement_updates: "auto"
-    allowed_updates:
-    - match:
-        update_type: "security"