Removed references to Lerna as it's not used

Signed-off-by: Andre Wanlin <awanlin@spotify.com>

docs/contribute/project-structure.md

@@ -221,7 +221,3 @@ future.
 
 - [`catalog-info.yaml`](https://github.com/backstage/backstage/tree/master/catalog-info.yaml) -
   Description of Backstage in the Backstage Entity format.
-
-- [`lerna.json`](https://github.com/backstage/backstage/tree/master/lerna.json) -
-  [Lerna](https://github.com/lerna/lerna) monorepo config. We are using
-  `yarn workspaces`, so this will only be used for executing scripts.

docs/getting-started/index.md

@@ -89,8 +89,8 @@ app
 - **package.json**: Root package.json for the project. _Note: Be sure that you
   don't add any npm dependencies here as they probably should be installed in
   the intended workspace rather than in the root._
-- **packages/**: Lerna leaf packages or "workspaces". Everything here is going
-  to be a separate package, managed by lerna.
+- **packages/**: Yarn workspaces, everything here is going
+  to be a separate package, managed by Yarn.
 - **packages/app/**: A fully functioning Backstage frontend app that acts as a
   good starting point for you to get to know Backstage.
 - **packages/backend/**: We include a backend that helps power features such as

docs/references/glossary.md

@@ -208,7 +208,7 @@ One of the [packages](#package) within a [monorepo](#monorepo). A package may or
 
 1. A single repository for a collection of related software projects, such as all projects belonging to an organization.
 
-2. A project layout that consists of multiple [packages](#package) within a single project, where packages are able to have local dependencies on each other. Often enabled through tooling such as [lerna](https://lerna.js.org/) and [yarn workspaces](https://classic.yarnpkg.com/en/docs/workspaces/)
+2. A project layout that consists of multiple [packages](#package) within a single project, where packages are able to have local dependencies on each other. Often enabled through tooling such as [yarn workspaces](https://classic.yarnpkg.com/en/docs/workspaces/)
 
 ## Name
 

lerna.json

@@ -1,6 +0,0 @@
-{
-  "packages": ["packages/*", "plugins/*"],
-  "npmClient": "yarn",
-  "useWorkspaces": true,
-  "version": "0.0.0"
-}

packages/config-loader/src/schema/collect.test.ts

@@ -41,16 +41,6 @@ describe('collectConfigSchemas', () => {
     mockDir.clear();
   });
 
-  it('should not find any schemas without packages', async () => {
-    mockDir.setContent({
-      'lerna.json': JSON.stringify({
-        packages: ['packages/*'],
-      }),
-    });
-
-    await expect(collectConfigSchemas([], [])).resolves.toEqual([]);
-  });
-
   it('should find schema in a local package', async () => {
     mockDir.setContent({
       node_modules: {