Purge `get-pip.py` from history

[marshallward]

At some point, I foolishly added a get-pip.py script to help with installation. But little did I know that this was a 1.7M file which was not so much a script as it was a binary embedded inside of a script.

At some point, I would like to purge this from the history. Given that it was a standalone script with no dependencies, it should be safe to remove. But there may be inevitable complaints from git about this rewriting of history.

Not suggesting we need to do this now, but it should be done "someday" in order to keep the repo size under control.