build: remove unreferenced tsconfig-build.json files (#30858)

These are no longer needed since Bazel generates a tsconfig for each compilation

PR Close #30858

packages/router/testing/tsconfig-build.json

@@ -1,28 +0,0 @@
-{
-  "extends": "../tsconfig-build.json",
-
-  "compilerOptions": {
-    "baseUrl": ".",
-    "rootDir": "../",
-    "paths": {
-      "@angular/core": ["../../../dist/packages/core"],
-      "@angular/common": ["../../../dist/packages/common"],
-      "@angular/common/testing": ["../../../dist/packages/common/testing"],
-      "@angular/platform-browser": ["../../../dist/packages/platform-browser"],
-      "@angular/router": ["../../../dist/packages/router"]
-    },
-    "outDir": "../../../dist/packages/router"
-  },
-
-  "files": [
-    "public_api.ts"
-  ],
-
-  "angularCompilerOptions": {
-    "annotateForClosureCompiler": true,
-    "strictMetadataEmit": false,
-    "skipTemplateCodegen": true,
-    "flatModuleOutFile": "testing.js",
-    "flatModuleId": "@angular/router/testing"
-  }
-}