mergify: remove mergify config on stable-4.0

This commit removes the mergify config on stable-4.0

At the moment there is no need to have a mergify config on this branch
given that we don't use it.

Signed-off-by: Guillaume Abrioux <gabrioux@redhat.com>

.mergify.yml

@@ -1,86 +0,0 @@
-pull_request_rules:
-  - name: automatic merge
-    conditions:
-      - label!=DNM
-      - '#approved-reviews-by>=1'
-      - 'status-success=Testing: ceph-ansible PR Pipeline'
-    actions:
-      merge:
-        method: rebase
-        rebase_fallback: merge
-        strict: smart
-      dismiss_reviews: {}
-      delete_head_branch: {}
-  - name: automatic merge on skip ci
-    conditions:
-      - label!=DNM
-      - title~=\[skip ci\]
-      - '#approved-reviews-by>=2'
-    actions:
-      merge:
-        method: rebase
-        rebase_fallback: merge
-        strict: smart
-      dismiss_reviews: {}
-      delete_head_branch: {}
-  - name: automerge backport 3.0
-    conditions:
-      - author=mergify[bot]
-      - base=stable-3.0
-      - label!=DNM
-      - 'status-success=Testing: ceph-ansible PR Pipeline'
-    actions:
-      merge:
-        method: rebase
-        rebase_fallback: merge
-        strict: smart
-      dismiss_reviews: {}
-      delete_head_branch: {}
-  - name: automerge backport 3.1
-    conditions:
-      - author=mergify[bot]
-      - base=stable-3.1
-      - label!=DNM
-      - 'status-success=Testing: ceph-ansible PR Pipeline'
-    actions:
-      merge:
-        method: rebase
-        rebase_fallback: merge
-        strict: smart
-      dismiss_reviews: {}
-      delete_head_branch: {}
-  - name: automerge backport 3.2
-    conditions:
-      - author=mergify[bot]
-      - base=stable-3.2
-      - label!=DNM
-      - 'status-success=Testing: ceph-ansible PR Pipeline'
-    actions:
-      merge:
-        method: rebase
-        rebase_fallback: merge
-        strict: smart
-      dismiss_reviews: {}
-      delete_head_branch: {}
-# Backports
-  - actions:
-      backport:
-        branches:
-        - stable-3.0
-    conditions:
-      - label=backport-stable-3.0
-    name: backport stable-3.0
-  - actions:
-      backport:
-        branches:
-        - stable-3.1
-    conditions:
-      - label=backport-stable-3.1
-    name: backport stable-3.1
-  - actions:
-      backport:
-        branches:
-        - stable-3.2
-    conditions:
-      - label=backport-stable-3.2
-    name: backport stable-3.2