fix: don’t raise error for locked private dependencies

yarn should be able to handle this now.

Closes #1721

lib/manager/npm/package.js

@@ -45,28 +45,6 @@ async function getPackageUpdates(config) {
         )}`
       );
     }
-  } else if (config.updateLockFiles && config.yarnLock) {
-    if (config.repoIsOnboarded) {
-      // Config error
-      const error = new Error('config-validation');
-      error.configFile = config.packageFile;
-      error.validationError = `Failed to look up npm dependency \`${
-        config.depName
-      }\``;
-      error.validationMessage =
-        'This dependency lookup failure will cause all lock file updates to fail. Please either remove the dependency, or remove the lock file, or add npm authentication, or set `updateLockFiles` to false in your config.';
-      throw error;
-    } else {
-      // If dependency lookup fails then error and return
-      const result = {
-        type: 'error',
-        message: `Failed to look up dependency ${
-          config.depName
-        }. This will prevent yarn.lock from being updated.`,
-      };
-      results = [result];
-      logger.info({ dependency: config.depName }, result.message);
-    }
   } else {
     // If dependency lookup fails then warn and return
     const result = {

test/manager/npm/__snapshots__/package.spec.js.snap

@@ -6,16 +6,6 @@ Array [
 ]
 `;
 
-exports[`lib/workers/package/npm getPackageUpdates returns error if no npm scoped dep found 1`] = `
-Array [
-  Object {
-    "message": "Failed to look up dependency @foo/something. This will prevent yarn.lock from being updated.",
-    "repositoryUrl": null,
-    "type": "error",
-  },
-]
-`;
-
 exports[`lib/workers/package/npm getPackageUpdates returns warning if no npm dep found 1`] = `
 Array [
   Object {

test/manager/npm/package.spec.js

@@ -48,25 +48,6 @@ describe('lib/workers/package/npm', () => {
       expect(res[0].type).toEqual('warning');
       expect(npmApi.getDependency.mock.calls.length).toBe(1);
     });
-    it('throws error if onboarded and no npm dep found and yarn.lock', async () => {
-      config.repoIsOnboarded = true;
-      config.yarnLock = 'some package lock';
-      let e;
-      try {
-        await npm.getPackageUpdates(config);
-      } catch (err) {
-        e = err;
-      }
-      expect(e).toBeDefined();
-    });
-    it('returns error if no npm scoped dep found', async () => {
-      config.repoIsOnboarded = false;
-      config.depName = '@foo/something';
-      config.yarnLock = '# some yarn lock';
-      const res = await npm.getPackageUpdates(config);
-      expect(res).toHaveLength(1);
-      expect(res).toMatchSnapshot();
-    });
     it('returns warning if warning found', async () => {
       npmApi.getDependency.mockReturnValueOnce({});
       versions.determineUpgrades = jest.fn(() => [