Remove npm shrinkwrap tasks

We're not maintaining the shrinkwrap as part of the repo, and it doesn't
add any value when being generated automatically as part of our build
process. In its current form, it actually makes it so we cannot
successfully create new builds without manually setting up a local
shrinkwrap first.

tasks/build/index.js

@@ -13,7 +13,6 @@ module.exports = function (grunt) {
     '_build:packageJson',
     '_build:readme',
     '_build:installNpmDeps',
-    '_build:shrinkwrap:ensureExists:true',
     'clean:testsFromModules',
     'clean:deepModuleBins',
     'clean:deepModules',

tasks/build/shrinkwrap.js

@@ -1,23 +0,0 @@
-module.exports = function (grunt) {
-  let { config } = grunt;
-  let { statSync } = require('fs');
-  let { join } = require('path');
-  let buildDir = join(config.get('root'), 'build', 'kibana');
-  let exec = (...args) => require('../utils/exec')(...args, { cwd: buildDir });
-  let newFiles = [];
-  let shrinkwrapFile = join(buildDir, 'npm-shrinkwrap.json');
-
-  grunt.registerTask('_build:shrinkwrap:ensureExists', function (createIfMissing) {
-    try {
-      statSync(shrinkwrapFile);
-    } catch (e) {
-      if (e.code !== 'ENOENT') throw e;
-
-      if (createIfMissing) {
-        exec('npm', ['shrinkwrap', '--dev', '--loglevel', 'error']);
-        newFiles.push(shrinkwrapFile);
-      }
-      else grunt.fail.warn('Releases require an npm-shrinkwrap.json file to exist');
-    }
-  });
-};

tasks/release.js

@@ -3,7 +3,6 @@ module.exports = function (grunt) {
 
   // build, then zip and upload to s3
   grunt.registerTask('release', [
-    '_build:shrinkwrap:ensureExists',
     '_release:confirmUpload',
     '_release:loadS3Config',
     'build',