Don't cache the file size

Don't cache the file size

Little point in caching the file size if you are going to update it
before using anyway.

Yes, in some edge cases, the accurate size might be unavailable, but I
don't think that there are many cases in which we can't check the file
size, but we can write to it. More importantly, the cached value was
wrong anyway, since log_print_log_line has been returning hogwash
instead of an accurate written byte count for some time.

Change-Id: I73d8b6d757ac0cd6574b66349ac2e8054bb15aaa