fix(cli): do not install deps for built-in connectors

Author: raymondfeng

packages/cli/generators/datasource/index.js

@@ -311,8 +311,10 @@ module.exports = class DataSourceGenerator extends ArtifactGenerator {
       debug(`npmModule - ${pkgs[0]}`);
     } else {
       const connectorName = this.artifactInfo.connector;
-      // Other connectors
-      if (!deps[connectorName]) pkgs.push(connectorName);
+      // Other connectors that are not listed in `connectors.json`.
+      // No install is needed for those in connectors.json but without a
+      // package name as they are built-in connectors
+      if (!deps[connectorName] && !connector) pkgs.push(connectorName);
     }
 
     if (!deps['@loopback/repository']) {

packages/cli/test/integration/generators/datasource.integration.js

@@ -157,6 +157,7 @@ function checkBasicDataSourceFiles() {
   assert.file(expectedTSFile);
   assert.file(expectedJSONFile);
   assert.file(expectedIndexFile);
+  assert.noFile(path.join(SANDBOX_PATH, 'node_modules/memory'));
 
   assert.fileContent(expectedTSFile, /import {inject} from '@loopback\/core';/);
   assert.fileContent(