Remove rejectionWarning logic

It's due to a bug introduced in Node 12.6.0 but fixed in 12.7.0

nodejs/node#28540

src/handle/common.js

@@ -1,6 +1,5 @@
 import { isLimited } from '../limit.js'
 import { isRepeated } from '../repeat.js'
-import { isRejectionWarning } from '../warnings.js'
 import { getLevel } from '../level.js'
 import { getError, addErrorPrint } from '../error/main.js'
 import { exitProcess } from '../exit.js'
@@ -34,10 +33,6 @@ export const handleEvent = async function({
     return
   }
 
-  if (isRejectionWarning(name, event)) {
-    return
-  }
-
   await logEvent({ opts, name, event })
 
   await exitProcess({ name, opts })

src/warnings.js

@@ -46,14 +46,3 @@ const getWarningListeners = function() {
 }
 
 const warningListener = getWarningListener()
-
-// Unhandled rejected promises emit a warning by default (unless
-// --unhandled-rejections is used). This warning is not useful, so we remove it.
-export const isRejectionWarning = function(name, { value }) {
-  return (
-    name === 'warning' &&
-    value instanceof Error &&
-    value.name === 'DeprecationWarning' &&
-    value.code === 'DEP0018'
-  )
-}