Fix WriteHTMLForTracesToFile

Turn out my last fix doesn't actually work. Somehow able to get a window machine to test this fix. Also clean up compressed_file logic which I believe is unnecessary.
To test this change on Windows, run:
python run_tests trace2html
Why does this seem wrong? We gzip the data and then base64 encode it.

@natduca would better be able to determine if zlib.compress(str) would be similar.