update default index priority for cold phase

Author: jloleysens

x-pack/plugins/index_lifecycle_management/__jest__/client_integration/edit_policy/edit_policy.test.ts

@@ -283,11 +283,7 @@ describe('<EditPolicy />', () => {
         const entirePolicy = JSON.parse(JSON.parse(latestRequest.requestBody).body);
         expect(entirePolicy.phases.cold).toMatchInlineSnapshot(`
           Object {
-            "actions": Object {
-              "set_priority": Object {
-                "priority": 50,
-              },
-            },
+            "actions": Object {},
             "min_age": "0d",
           }
         `);

x-pack/plugins/index_lifecycle_management/public/application/sections/edit_policy/form_schema.ts

@@ -284,7 +284,6 @@ export const schema: FormSchema<FormInternal> = {
         },
         set_priority: {
           priority: {
-            defaultValue: defaultPhaseIndexPriority as any,
             label: i18nTexts.editPolicy.setPriorityFieldLabel,
             validations: [{ validator: ifExistsNumberNonNegative }],
             serializer: serializers.stringToNumber,