[minor]: remove openapi.yaml

openapi.yaml

-# Generated with protoc-gen-openapi
-# https://github.com/google/gnostic/tree/master/cmd/protoc-gen-openapi
-
-openapi: 3.0.3
-info:
-    title: Greeter API
-    description: The greeting service definition.
-    version: 0.0.1
-paths:
-    /helloworld/{name}:
-        get:
-            tags:
-                - Greeter
-            description: Sends a greeting
-            operationId: Greeter_SayHello
-            parameters:
-                - name: name
-                  in: path
-                  required: true
-                  schema:
-                    type: string
-            responses:
-                "200":
-                    description: OK
-                    content:
-                        application/json:
-                            schema:
-                                $ref: '#/components/schemas/helloworld.v1.HelloReply'
-components:
-    schemas:
-        helloworld.v1.HelloReply:
-            type: object
-            properties:
-                message:
-                    type: string
-            description: The response message containing the greetings
-tags:
-    - name: Greeter