Fix presubmits for Python 3

Calls to "python" won't work on vanilla MacOS installs (nor many
distributions of Linux), and AFAICT we're assuming it refers to python3
anyways.

xreadlines was removed in Python 3, and the suggested equivalent is to
use the file directly as an iterator:
https://docs.python.org/2.7/library/stdtypes.html#file.xreadlines

Change-Id: Iae51e3923e38ea63f857a17b9ff80e79871efee5
Reviewed-on: https://skia-review.googlesource.com/c/skia/+/537982
Reviewed-by: Kevin Lubick <kjlubick@google.com>
Commit-Queue: James Godfrey-Kittle <jamesgk@google.com>
1 file changed