python_package_*_pip E parameter - misleading docs and possible failures

[llnz]

The docstrings for the pythonpackage*_pip methods talk about the E parameter and how it is passed to pip as -E.

Only upgrade and remove actually have E parameters, and only upgrade uses it by passing it to pip.

But pip (at least on my system) doesn't take an -E argument.

I suggest that it's removed from the docs, the function parameters and the code of python_package_upgrade_pip

[sebastien]

Good catch, the PIP package is a contribution so I didn't check it too much, sadly. Thanks!