Migrate all remaining fixtures to jest expect

packages/babel-plugin-transform-react-jsx-source/test/fixtures/react-source/basic-sample/exec.js

@@ -11,4 +11,4 @@ var expected = multiline([
   '}} />;',
 ]);
 
-assert.equal(actual, expected);
+expect(actual).toBe(expected);

packages/babel-plugin-transform-react-jsx-source/test/fixtures/react-source/with-source/exec.js

@@ -5,4 +5,4 @@ var actual = transform(
 
 var expected = 'var x = <sometag __source="custom" />;';
 
-assert.equal(actual, expected);
+expect(actual).toBe(expected);