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/core/testing/tsconfig-build.json

@@ -1,31 +0,0 @@
-{
-  "extends": "../tsconfig-build.json",
-  "compilerOptions": {
-    "baseUrl": ".",
-    "rootDir": "../",
-    "paths": {
-      "rxjs/*": [
-        "../../../node_modules/rxjs/*"
-      ],
-      "@angular/core": [
-        "../../../dist/packages/core"
-      ],
-      "@angular/compiler": [
-        "../../../dist/packages/compiler"
-      ],
-    },
-    "outDir": "../../../dist/packages/core"
-  },
-  "files": [
-    "public_api.ts",
-    "../../../node_modules/zone.js/dist/zone.js.d.ts",
-    "../../system.d.ts",
-    "../../types.d.ts"
-  ],
-  "angularCompilerOptions": {
-    "strictMetadataEmit": false,
-    "skipTemplateCodegen": true,
-    "flatModuleOutFile": "testing.js",
-    "flatModuleId": "@angular/core/testing"
-  }
-}