Fix two typos.

1. Removes extra "and". Link to the [page](https://developers.google.com/web/fundamentals/performance/critical-rendering-path/constructing-the-object-model).
2. Uses correct number for saved KB based on [image](https://developers.google.com/web/fundamentals/performance/optimizing-content-efficiency/images/transfer-vs-actual-size.png). Link to the [page](https://developers.google.com/web/fundamentals/performance/optimizing-content-efficiency/optimize-encoding-and-transfer#text-compression-with-gzip).