Don't merge test options. (#6157)

* Don't merge test options.

Particularly, I don't want `lodash/merge` to merge my specific plugins
with the general test plugins. It led to odd behavior where I could
enable a loose transform in my specific test, just to have it overridden
by the test fixture's general options.

* Need options

packages/babel-plugin-transform-object-rest-spread/test/fixtures/object-rest/symbol-exec/options.json

@@ -1,6 +1,3 @@
 {
-  "parserOpts": {
-    "allowReturnOutsideFunction": true
-  },
-  "plugins": [ "transform-es2015-destructuring" ]
+  "plugins": [ "transform-es2015-destructuring", "transform-object-rest-spread" ]
 }