strip comments when re-emitting tsconfig.json (#10529)

src/harness/unittests/tsconfigParsing.ts

@@ -186,6 +186,7 @@ namespace ts {
             const content = `{
                 "compilerOptions": {
                     "allowJs": true
+                    // Some comments
                     "outDir": "bin"
                 }
                 "files": ["file1.ts"]

src/services/utilities.ts

@@ -930,7 +930,8 @@ namespace ts {
         const options: TranspileOptions = {
             fileName: "config.js",
             compilerOptions: {
-                target: ScriptTarget.ES6
+                target: ScriptTarget.ES6,
+                removeComments: true
             },
             reportDiagnostics: true
         };