[`pyflakes`] Improve `invalid-print-syntax` documentation (#11171)
This syntax wasn't "deprecated" in Python 3; it was removed.
I started looking at this rule because I was curious how Ruff could even
detect this without a Python 2 parser. Then I realized that
"print >> f, x" is actually valid Python 3 syntax: it creates a tuple
containing a right-shifted version of the print function.
