Don't include _unittest.py files in `grit_info --inputs` output.

Don't include _unittest.py files in `grit_info --inputs` output.

If only a test changes, it shouldn't affect the files created by grit, so
this is useless output.

Reduces the size of chrome's ninja files by about 120kB / 1%.

r144

[Nico, 2014-01-08 00:50:00]

Committed as r144 (looks like joi's lgtm didn't make it through to rietveld, but
he lg'd over email)

[Jói, 2014-01-08 09:07:55]

On 2014/01/08 00:50:00, Nico wrote:
> Committed as r144 (looks like joi's lgtm didn't make it through to rietveld,
but
> he lg'd over email)

LGTM for the record.