chore: remove unused promisify code (#21114)

spec-main/api-deprecate-spec.ts

@@ -192,79 +192,4 @@ describe('deprecate', () => {
       expect(warnings[0]).to.equal('\'old\' is deprecated and will be removed. Please use \'new\' instead.')
     })
   })
-
-  describe('promisify', () => {
-    const expected = 'Hello, world!'
-    let promiseFunc: (param: any) => Promise<any>
-    let warnings: string[]
-
-    const enableCallbackWarnings = () => {
-      warnings = []
-      deprecate.setHandler(warning => warnings.push(warning))
-      process.enablePromiseAPIs = true
-    }
-
-    beforeEach(() => {
-      deprecate.setHandler(null)
-      process.throwDeprecation = true
-
-      promiseFunc = param => new Promise((resolve) => resolve(param))
-    })
-
-    it('acts as a pass-through for promise-based invocations', async () => {
-      enableCallbackWarnings()
-      promiseFunc = deprecate.promisify(promiseFunc)
-
-      const actual = await promiseFunc(expected)
-      expect(actual).to.equal(expected)
-      expect(warnings).to.have.lengthOf(0)
-    })
-
-    it('only calls back an error if the callback is called with (err, data)', async () => {
-      enableCallbackWarnings()
-      const erringPromiseFunc = deprecate.promisify(
-        () => new Promise((resolve, reject) => {
-          reject(new Error('fail'))
-        })
-      )
-
-      {
-        const [err, data] = await new Promise(resolve => {
-          (erringPromiseFunc as any)((err: Error | undefined, data: any) => {
-            resolve([err, data])
-          }).catch(() => { /* silence deprecation warning */ })
-        })
-        expect(data).to.be.undefined()
-        expect(err).to.be.an.instanceOf(Error).with.property('message', 'fail')
-      }
-      {
-        const data = await new Promise(resolve => {
-          (erringPromiseFunc as any)((data: any) => { resolve(data) })
-            .catch(() => { /* silence deprecation warning */ })
-        })
-        expect(data).to.be.undefined()
-      }
-    })
-
-    it('warns exactly once for callback-based invocations', (done) => {
-      enableCallbackWarnings()
-      promiseFunc = deprecate.promisify(promiseFunc)
-
-      let callbackCount = 0
-      const invocationCount = 3
-      const callback = (actual: number) => {
-        expect(actual).to.equal(expected)
-        expect(warnings).to.have.lengthOf(1)
-        expect(warnings[0]).to.include('promiseFunc')
-        callbackCount += 1
-        if (callbackCount === invocationCount) {
-          done()
-        }
-      }
-
-      for (let i = 0; i < invocationCount; i += 1) {
-        (promiseFunc as any)(expected, callback)
-      }
-    })
-  })
 })