fix(lifecycle): don't set NODE_PRESERVE_SYMLINKS to 1

With the new store and node_modules structure the pnpm leverages
symlinks preserving is not only unnecessary, it hurts.

src/runScript.ts

@@ -56,6 +56,5 @@ function createEnv (cwd: string) {
     path.dirname(process.execPath),
     process.env[PATH]
   ].join(path.delimiter)
-  env['NODE_PRESERVE_SYMLINKS'] = '1'
   return env
 }

test/index.ts

@@ -5,4 +5,3 @@ import './uninstall'
 import './link'
 import './prune'
 import './cache'
-import './run'

test/run.ts

@@ -1,35 +0,0 @@
-import tape = require('tape')
-import promisifyTape from 'tape-promise'
-const test = promisifyTape(tape)
-import semver = require('semver')
-import fs = require('mz/fs')
-import prepare from './support/prepare'
-import testDefaults from './support/testDefaults'
-import {installPkgs} from '../lib'
-import runCmd from '../lib/cmd/run'
-
-const preserveSymlinksEnvVariable = semver.satisfies(process.version, '>=7.1.0')
-
-test('run node in scripts with preserve symlinks mode', async function (t) {
-  if (!preserveSymlinksEnvVariable) {
-    t.skip('this test is only for Node.js >= 7.1.0')
-    return
-  }
-
-  prepare(t, {
-    scripts: {
-      test: 'node index'
-    }
-  })
-
-  await fs.writeFile('index.js', `
-    const fs = require('fs')
-    const symlinksPreserved = require('symlinks-preserved')
-    fs.writeFileSync('test-result', symlinksPreserved, 'utf8')
-  `, 'utf8')
-
-  await installPkgs(['symlinks-preserved'], testDefaults())
-  const result = runCmd(['test'], {})
-  t.equal(result.status, 0, 'executable exited with success')
-  t.equal(await fs.readFile('test-result', 'utf8'), 'true', 'symlinks are preserved')
-})