feat(upgrade): use ComponentFactory.inputs/outputs/ngContentSelectors (#15214)

DEPRECATION:
- the arguments `inputs` / `outputs` / `ngContentSelectors` of `downgradeComponent`
  are no longer used as Angular calculates these automatically now.
- Compiler.getNgContentSelectors is deprecated. Use
  ComponentFactory.ngContentSelectors instead.

packages/compiler/src/metadata_resolver.ts

@@ -156,7 +156,6 @@ export class CompileMetadataResolver {
         const templateName = inputs[propName];
         factory.inputs.push({propName, templateName});
       }
-      const outputsArr: {propName: string, templateName: string}[] = [];
       for (let propName in outputs) {
         const templateName = outputs[propName];
         factory.outputs.push({propName, templateName});

packages/compiler/test/aot/compiler_spec.ts

@@ -324,7 +324,6 @@ describe('compiler (unbundled Angular)', () => {
          const host = new MockCompilerHost(['/app/app.ts'], FILES, angularFiles);
          const aotHost = new MockAotCompilerHost(host);
          let generatedFiles: GeneratedFile[];
-         const warnSpy = spyOn(console, 'warn');
          compile(host, aotHost, expectNoDiagnostics).then((generatedFiles) => {
            const genFile = generatedFiles.find(genFile => genFile.srcFileUrl === '/app/app.ts');
            const createComponentFactoryCall =