remove drone (replaced by github ci)

.drone.yml

@@ -1,37 +0,0 @@
----
-kind: pipeline
-name: nixos-tests
-
-steps:
-- name: test
-  image: busybox
-  environment:
-    NIX_REMOTE: daemon
-    PATH: /nix/var/nix/profiles/system/sw/bin/
-    PAGER: cat
-    USER: root
-  volumes:
-    - name: nixstore
-      path: /nix
-    - name: nixconf
-      path: /etc/nix
-    - name: sslcerts
-      path: /etc/ssl
-  commands:
-  - nix-build -I nixpkgs=https://github.com/NixOS/nixpkgs/archive/nixpkgs-unstable.tar.gz -A sops-install-secrets.tests
-  - nix-build -I nixpkgs=https://github.com/NixOS/nixpkgs/archive/nixos-20.09.tar.gz -A sops-install-secrets.tests
-volumes:
-- name: nixstore
-  host:
-    path: /nix
-- name: nixconf
-  host:
-    path: /nix/var/nix/profiles/system/etc/nix
-- name: sslcerts
-  host:
-    path: /nix/var/nix/profiles/system/etc/ssl
----
-kind: signature
-hmac: 5bb657faca0ecd18576534f7e486511d6f698595cc244d9617e660ef2ddb678d
-
-...