docs(api): stop requiring priority on the channel rule items

The silence, inhibit and unsubscribe rule item schemas dropped their
`priority` property when the field left the API, but kept `priority` in
their `required` list. The schemas then demanded a key the endpoints
never return — including in their own response examples.

Remove the three stale required entries.

Author: ysyneu

api-reference/on-call.openapi.en.json

@@ -23606,7 +23606,6 @@
         "required": [
           "account_id",
           "channel_id",
-          "priority",
           "rule_name",
           "description",
           "source_filters",
@@ -27285,7 +27284,6 @@
         "required": [
           "account_id",
           "channel_id",
-          "priority",
           "rule_name",
           "description",
           "time_filters",
@@ -28386,7 +28384,6 @@
         "required": [
           "account_id",
           "channel_id",
-          "priority",
           "rule_name",
           "description",
           "filters",

api-reference/on-call.openapi.zh.json

@@ -23597,7 +23597,6 @@
         "required": [
           "account_id",
           "channel_id",
-          "priority",
           "rule_name",
           "description",
           "source_filters",
@@ -27276,7 +27275,6 @@
         "required": [
           "account_id",
           "channel_id",
-          "priority",
           "rule_name",
           "description",
           "time_filters",
@@ -28377,7 +28375,6 @@
         "required": [
           "account_id",
           "channel_id",
-          "priority",
           "rule_name",
           "description",
           "filters",

api-reference/openapi.en.json

@@ -35839,7 +35839,6 @@
         "required": [
           "account_id",
           "channel_id",
-          "priority",
           "rule_name",
           "description",
           "time_filters",
@@ -35937,7 +35936,6 @@
         "required": [
           "account_id",
           "channel_id",
-          "priority",
           "rule_name",
           "description",
           "source_filters",
@@ -36022,7 +36020,6 @@
         "required": [
           "account_id",
           "channel_id",
-          "priority",
           "rule_name",
           "description",
           "filters",

api-reference/openapi.zh.json

@@ -35830,7 +35830,6 @@
         "required": [
           "account_id",
           "channel_id",
-          "priority",
           "rule_name",
           "description",
           "time_filters",
@@ -35928,7 +35927,6 @@
         "required": [
           "account_id",
           "channel_id",
-          "priority",
           "rule_name",
           "description",
           "source_filters",
@@ -36013,7 +36011,6 @@
         "required": [
           "account_id",
           "channel_id",
-          "priority",
           "rule_name",
           "description",
           "filters",