Use type generator binary instead of gulp script.

The type generator can now verify types all by itself, so it's simpler
to just use this flag than to integrate with gulp.

Also bump package-lock to pick up latest Analyzer release, which fixes a
bug that was causing the type generator to throw an exception relating
to enqueueDebouncer.

gulpfile.js

@@ -115,16 +115,6 @@ gulp.task('generate-externs', gulp.series('clean', async () => {
   await fs.writeFile('externs/closure-types.js', `${header}${declarations}`);
 }));
 
-gulp.task('generate-typescript', async () => {
-  let genTs = require('@polymer/gen-typescript-declarations').generateDeclarations;
-  await del(['**/*.d.ts', '!interfaces.d.ts', '!node_modules/**']);
-  const config = await fs.readJson(path.join(__dirname, 'gen-tsd.json'));
-  const files = await genTs(__dirname, config);
-  for (const [filePath, contents] of files) {
-    await fs.outputFile(path.join(__dirname, filePath), contents);
-  }
-});
-
 const runClosureOnly = ({lintOnly}) => () => {
   let entry, splitRx, joinRx, addClosureTypes;
 
@@ -274,7 +264,6 @@ gulp.task('lint-eslint', function() {
 gulp.task('lint', gulp.series('lint-eslint'));
 
 // TODO(timvdlippe): Add back `'generate-externs',` once we can generate externs again
-gulp.task('generate-types', gulp.series('generate-typescript'));
 
 gulp.task('update-version', () => {
   return gulp.src('lib/utils/boot.js')