Removed polyfill code for node <16

They are no longer supported:

brianc#3483 (comment)

Author: bitifet

packages/pg-native/bench/leaks.js

@@ -1,15 +1,6 @@
 const Client = require('../')
 const async = require('async')
 
-let performance
-try {
-  // Support for node < 16.0.0
-  performance = require('perf_hooks').performance
-} catch (e) {
-  // failback for node < 8.5.0
-  performance = { now: Date.now } // Fallback to Date.now
-}
-
 const loop = function () {
   const client = new Client()
 

packages/pg-protocol/src/b.ts

@@ -2,15 +2,6 @@
 
 import { BufferReader } from './buffer-reader'
 
-let performance: { now: () => number }
-try {
-  // Support for node < 16.0.0
-  performance = require('perf_hooks').performance
-} catch (e) {
-  // failback for node < 8.5.0
-  performance = { now: Date.now } // Fallback to Date.now
-}
-
 const LOOPS = 1000
 let count = 0
 const start = performance.now()

packages/pg/bench.js

@@ -1,14 +1,5 @@
 const pg = require('./lib')
 
-let performance
-try {
-  // Support for node < 16.0.0
-  performance = require('perf_hooks').performance
-} catch (e) {
-  // failback for node < 8.5.0
-  performance = { now: () => Date.now() }
-}
-
 const params = {
   text: 'select typname, typnamespace, typowner, typlen, typbyval, typcategory, typispreferred, typisdefined, typdelim, typrelid, typelem, typarray from pg_type where typtypmod = $1 and typisdefined = $2',
   values: [-1, true],