test(@angular-devkit/build-angular): remove invalid project extensions from test projects

This causes logs to be printed during test runs.

Author: alan-agius4

packages/angular_devkit/build_angular/test/hello-world-app/angular.json

@@ -8,7 +8,6 @@
     }
   },
   "schematics": {},
-  "targets": {},
   "projects": {
     "app": {
       "root": "src",

packages/angular_devkit/build_webpack/test/angular-app/angular.json

@@ -8,7 +8,6 @@
     }
   },
   "schematics": {},
-  "targets": {},
   "projects": {
     "app": {
       "root": "src",

packages/angular_devkit/build_webpack/test/basic-app/angular.json

@@ -4,7 +4,6 @@
   "newProjectRoot": "./projects",
   "cli": {},
   "schematics": {},
-  "targets": {},
   "projects": {
     "app": {
       "root": "src",