Remove vendored colorama

[ichard26]

Pip's internal codebase doesn't use colorama anywhere. It was kept around for rich, but rich 12+ doesn't need it (opting to issue the appropriate Win32 API calls itself). pygments still imports colorama, but it's an optional dependency for the command line interface which pip evidently doesn't use.

~/dev/oss/pip ❯ git grep "colorama" **.py
src/pip/_internal/cli/spinners.py:    # even via colorama. So don't even try.
src/pip/_vendor/pygments/cmdline.py:        # unfortunately colorama doesn't support binary streams on Py3
src/pip/_vendor/pygments/cmdline.py:            import pip._vendor.colorama.initialise as colorama_initialise
src/pip/_vendor/pygments/cmdline.py:            outfile = colorama_initialise.wrap_stream(

Textualize/rich#1993