fix(abstract-utxo): fix mocha config

Old config ran all tests by default when used from IntelliJ

Issue: BTC-1450

Author: OttoAllmendinger

modules/abstract-utxo/.mocharc.js

@@ -2,7 +2,5 @@
 
 module.exports = {
   require: 'ts-node/register',
-  timeout: '2000',
-  exit: true,
-  spec: ['test/**/*.ts'],
+  extension: ['.js', '.ts'],
 };