core/api: move to core/proto

This is keeping in line with conventions that protobuf files generally
live in a 'proto/' directory. Even without that, a lot of the protos in
there aren't actually part of an API, so keeping them in `api/` is a bit
of a misnomer.

We also remove unused protos that were part of the old
integrity/lifecycle flow. Again, these will make a comeback.

Test Plan: this should fail. part of a larger stack. D590 is the first tip of the stack that should work.

X-Origin-Diff: phab/D588
GitOrigin-RevId: 4a7af494810348f6bcabd49e63902b4c47e6ec35
diff --git a/core/proto/common/common.proto b/core/proto/common/common.proto
new file mode 100644
index 0000000..5616103
--- /dev/null
+++ b/core/proto/common/common.proto
@@ -0,0 +1,24 @@
+// Copyright 2020 The Monogon Project Authors.
+//
+// SPDX-License-Identifier: Apache-2.0
+//
+// 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.
+
+syntax = "proto3";
+package smalltown.core.proto.common;
+option go_package = "git.monogon.dev/source/nexantic.git/core/proto/common";
+
+enum TrustBackend {
+    DUMMY = 0;
+    TPM = 1;
+}