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
There actually is something wrong with this code - you can't open a file for writing multiple times on Windows. `NamedTemporaryFile()` and `gzip.open()` both open the same file, leading to this stack trace:

```
WriteToFile at third_party\trace-viewer\trace_viewer\build\trace2html.py:57
  gzfile = gzip.open(compressed_file.name, 'wb')
open at E:\b\depot_tools\python276_bin\lib\gzip.py:34
  return GzipFile(filename, mode, compresslevel)
__init__ at E:\b\depot_tools\python276_bin\lib\gzip.py:94
  fileobj = self.myfileobj = __builtin__.open(filename, mode or 'rb')
IOError: [Errno 13] Permission denied: 'c:\\users\\chrome~2\\appdata\\local\\temp\\tmpdqtn5x'
```