Allow building without python2 (#8605)
Allow building without python2 (#8605)

Almost all of the python build files in the flutter project work if
`python` is `python2` or `python3`. This is the only area where print is
incorrectly used (for `python3`).

Related issue: https://fuchsia-review.googlesource.com/c/fuchsia/+/272925
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