Re-enable Watcher rest test (elastic#47699)

This test is believed to be fixed by elastic#43939

closes elastic#43988

Author: jakelandis

x-pack/qa/smoke-test-watcher/src/test/resources/rest-api-spec/test/painless/20_minimal_body.yml

@@ -1,8 +1,6 @@
 ---
 "Test execute watch api with minimal body":
-  - skip:
-      version: "all"
-      reason: "AwaitsFix https://github.com/elastic/elasticsearch/issues/43988"
+
   - do:
       cluster.health:
           wait_for_status: green