Remove italic style from HTML script tags

Remove italic style from script tags in Extended and Extended Light to match original Monokai theme and resolve #39.

I'm not familiar with editing ST themes but these changes seems to do the job. The containing `<dict>` tag now seems to be redundant and I noticed that the same result can be achieved by removing it entirely. I didn't go quite that far though as I wasn't sure if it would have a knock-on effect elsewhere.