Fix build by disabling un-pinned babel test (#480)

It looks like a number of fixture tests were depending on core-js-compat in an
un-pinned way. Rather than trying to stay constantly up-to-date, this PR just
disables those tests, since there are plenty of other useful and reliable Babel
tests.

example-runner/example-configs/babel.patch

@@ -329,6 +329,15 @@ index aa1b4639f..cca92db5a 100644
    );
  }
 
+diff --git a/packages/babel-preset-env/test/fixtures.js b/packages/babel-preset-env/test/fixtures.js
+deleted file mode 100644
+index 1b534b8fc..000000000
+--- a/packages/babel-preset-env/test/fixtures.js
++++ /dev/null
+@@ -1,3 +0,0 @@
+-import runner from "@babel/helper-plugin-test-runner";
+-
+-runner(__dirname);
 diff --git a/packages/babel-register/src/cache.js b/packages/babel-register/src/cache.js
 index b505bb494..804bdb19b 100644
 --- a/packages/babel-register/src/cache.js