Remove dependabot

This is done out of preference. We don't need our pull requests being flooded.

.github/dependabot.yml

@@ -1,27 +0,0 @@
-#
-# Copyright 2021 The Sigstore Authors.
-#
-# Licensed under the Apache License, Version 2.0 (the "License");
-# you may not use this file except in compliance with the License.
-# You may obtain a copy of the License at
-#
-#     http://www.apache.org/licenses/LICENSE-2.0
-#
-# Unless required by applicable law or agreed to in writing, software
-# distributed under the License is distributed on an "AS IS" BASIS,
-# WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
-# See the License for the specific language governing permissions and
-# limitations under the License.
-
-version: 2
-updates:
-  - package-ecosystem: npm
-    directory: "/"
-    schedule:
-      interval: "daily"
-    open-pull-requests-limit: 10
-  - package-ecosystem: "github-actions"
-    directory: "/"
-    schedule:
-      interval: "daily"
-    open-pull-requests-limit: 10