encoding/openapi: few tweaks in the output

- use oneOf instead of anyOf, as all values are
  derived from proto anyway for now.
- don't include empty list default

Change-Id: Ifd22e6f8bbd7d168123d00cc596cd7bb83ac517f
Reviewed-on: https://cue-review.googlesource.com/c/cue/+/2349
Reviewed-by: Marcel van Lohuizen <mpvl@golang.org>
diff --git a/encoding/openapi/testdata/openapi.json b/encoding/openapi/testdata/openapi.json
index c6cc8cb..7409a75 100644
--- a/encoding/openapi/testdata/openapi.json
+++ b/encoding/openapi/testdata/openapi.json
@@ -16,8 +16,7 @@
                         "type": "array",
                         "items": {
                            "type": "string"
-                        },
-                        "default": []
+                        }
                      },
                      "foo": {
                         "allOf": [
@@ -39,7 +38,7 @@
                },
                {
                   "type": "object",
-                  "anyOf": [
+                  "oneOf": [
                      {
                         "type": "object",
                         "required": [
@@ -81,8 +80,7 @@
                   "type": "array",
                   "items": {
                      "type": "integer"
-                  },
-                  "default": []
+                  }
                },
                "port": {
                   "type": "integer"
@@ -95,7 +93,7 @@
             "maximum": 2147483647
          },
          "YourMessage": {
-            "anyOf": [
+            "oneOf": [
                {
                   "type": "object",
                   "required": [
@@ -129,7 +127,7 @@
          "YourMessage2": {
             "allOf": [
                {
-                  "anyOf": [
+                  "oneOf": [
                      {
                         "type": "object",
                         "required": [
@@ -155,7 +153,7 @@
                   ]
                },
                {
-                  "anyOf": [
+                  "oneOf": [
                      {
                         "type": "object",
                         "required": [
@@ -181,7 +179,7 @@
                   ]
                },
                {
-                  "anyOf": [
+                  "oneOf": [
                      {
                         "type": "object",
                         "required": [
@@ -209,7 +207,7 @@
             ]
          },
          "Msg2": {
-            "anyOf": [
+            "oneOf": [
                {
                   "type": "object",
                   "required": [
@@ -255,7 +253,7 @@
          "DefaultStruct": {
             "allOf": [
                {
-                  "anyOf": [
+                  "oneOf": [
                      {
                         "$ref": "#/components/schema/Port"
                      },