Remove travis-python references as well as some unnecessary dependencies (#47209)
Summary:
This PR attempts to remove unneeded installations of `pip` among other packages in `install_base.sh` since these very same packages are already installed elsewhere (for example in `install_conda.sh`).
In the process, I found some old `TRAVIS_PYTHON_VERSION` references that are no longer needed, so I removed all references that need `install_travis_python.sh`
Pull Request resolved: https://github.com/pytorch/pytorch/pull/47209
Reviewed By: mruberry
Differential Revision: D24690079
Pulled By: janeyx99
fbshipit-source-id: f8fef4cda9832c868595d4745d811fc7d42df34d
