fix(@schematics/angular): remove downlevelIteration from tsconfig.json for new workspaces

We no longer need `downlevelIteration` as ES5 is output is no longer supported by the CLI.

(cherry picked from commit c7b7e59)

Author: alan-agius4

packages/schematics/angular/workspace/files/tsconfig.json.template

@@ -12,7 +12,6 @@
     "esModuleInterop": true,
     "sourceMap": true,
     "declaration": false,
-    "downlevelIteration": true,
     "experimentalDecorators": true,
     "moduleResolution": "node",
     "importHelpers": true,