raise onDidChange only when needed

src/monaco.contribution.ts

@@ -79,15 +79,21 @@ export class LanguageServiceDefaultsImpl implements monaco.languages.typescript.
 		return {
 			dispose: () => {
 				if (paths.length > 0) {
+					let changed = false;
+
 					paths.forEach(filePath => {
-						delete this._extraLibs[filePath];
+						if (delete this._extraLibs[filePath]) {
+							changed = true;
+						}
 					});
 
+					if (changed) {
 						this._onDidChange.fire(this);
 					}
 				}
 			}
 		}
+	}
 
 	getCompilerOptions(): monaco.languages.typescript.CompilerOptions {
 		return this._compilerOptions;